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1.  Feasibility, Yield, and Cost of Active Tuberculosis Case Finding Linked to a Mobile HIV Service in Cape Town, South Africa: A Cross-sectional Study 
PLoS Medicine  2012;9(8):e1001281.
Katharina Kranzer and colleagues investigate the operational characteristics of an active tuberculosis case-finding service linked to a mobile HIV testing unit that operates in underserviced areas in Cape Town, South Africa.
Background
The World Health Organization is currently developing guidelines on screening for tuberculosis disease to inform national screening strategies. This process is complicated by significant gaps in knowledge regarding mass screening. This study aimed to assess feasibility, uptake, yield, treatment outcomes, and costs of adding an active tuberculosis case-finding program to an existing mobile HIV testing service.
Methods and Findings
The study was conducted at a mobile HIV testing service operating in deprived communities in Cape Town, South Africa. All HIV-negative individuals with symptoms suggestive of tuberculosis, and all HIV-positive individuals regardless of symptoms were eligible for participation and referred for sputum induction. Samples were examined by microscopy and culture. Active tuberculosis case finding was conducted on 181 days at 58 different sites. Of the 6,309 adults who accessed the mobile clinic, 1,385 were eligible and 1,130 (81.6%) were enrolled. The prevalence of smear-positive tuberculosis was 2.2% (95% CI 1.1–4.0), 3.3% (95% CI 1.4–6.4), and 0.4% (95% CI 1.4 015–6.4) in HIV-negative individuals, individuals newly diagnosed with HIV, and known HIV, respectively. The corresponding prevalence of culture-positive tuberculosis was 5.3% (95% CI 3.5–7.7), 7.4% (95% CI 4.5–11.5), 4.3% (95% CI 2.3–7.4), respectively. Of the 56 new tuberculosis cases detected, 42 started tuberculosis treatment and 34 (81.0%) completed treatment. The cost of the intervention was US$1,117 per tuberculosis case detected and US$2,458 per tuberculosis case cured. The generalisability of the study is limited to similar settings with comparable levels of deprivation and TB and HIV prevalence.
Conclusions
Mobile active tuberculosis case finding in deprived populations with a high burden of HIV and tuberculosis is feasible, has a high uptake, yield, and treatment success. Further work is now required to examine cost-effectiveness and affordability and whether and how the same results may be achieved at scale.
Editors' Summary
Background
In 2010, 8.8 million people developed active tuberculosis—a contagious bacterial infection—and 1.4 million people died from the disease. Most of these deaths were in low- and middle-income countries and a quarter were in HIV-positive individuals—people who are infected with HIV, the virus that causes AIDS, are particularly susceptible to tuberculosis because of their weakened immune system. Tuberculosis is caused by Mycobacterium tuberculosis, which is spread in airborne droplets when people with the disease cough or sneeze. Its characteristic symptoms are a persistent cough, unintentional weight loss, hemoptysis (coughing up blood from the lungs), fever, and night sweats. Diagnostic tests for tuberculosis include sputum smear microscopy (microscopic analysis of mucus brought up from the lungs by coughing) and culture (growth) of M. tuberculosis from sputum samples. Tuberculosis can be cured by taking several powerful antibiotics daily for at least 6 months.
Why Was This Study Done?
To improve tuberculosis control, active disease must be diagnosed quickly and treated immediately. Passive tuberculosis case finding, which relies on people seeking medical help because they feel unwell, delays the diagnosis and treatment of tuberculosis and increases M. tuberculosis transmission. By contrast, active tuberculosis case finding—where health workers seek out and diagnose individuals with TB who have not sought care on their own initiative—has the potential to reduce tuberculosis transmission by improving case detection. The World Health Organization (WHO), which already recommends active tuberculosis case finding in HIV-infected individuals as part of its HIV/TB “Three I's” strategy, is currently developing guidelines to inform the design of national tuberculosis screening strategies based on the local prevalence of HIV and TB and other context-specific factors that affect how many individuals need to be screened to identify each additional new tuberculosis case (the “yield” of active case finding). Large gaps in our knowledge about mass-screening strategies are complicating the development of these guidelines so, in this observational prospective study, the researchers assess the feasibility, uptake, yield, treatment outcomes, and costs of adding an active tuberculosis case-finding program to an existing mobile HIV testing service in South Africa.
What Did the Researchers Do and Find?
All HIVnegative adults with symptoms characteristic of tuberculosis and all HIV-positive adults regardless of symptoms who attended a mobile HIV testing service operating in deprived communities in ape Town, South Africa between May 2009 and February 2011 were eligible for inclusion in the study. Of the 6,309 adults who accessed the mobile clinic during this period, 1,385 met these eligibility criteria, and 1,130 were enrolled and referred for the collection of sputum samples, which were analyzed by microscopy and culture. The prevalence of smear-positive tuberculosis was 2.2%, 3.3%, and 0.4% among HIV-negative study participants, newly diagnosed HIV-positive participants, and people already known to have HIV, respectively. The corresponding prevalences for smear-negative/culture-positive tuberculosis were 5.3%, 7.4%, and 4.3%, respectively (culture detects more tuberculosis cases than microscopy but, whereas microscopy can provide a result within 1–2 days, culture can take several weeks). Fifty-six new tuberculosis cases were identified, 42 people started tuberculosis treatment, and 34 completed treatment (a treatment success rate of 81%). Finally, the incremental cost of the intervention was US$1,117 per tuberculosis case detected and US$2,458 per tuberculosis case cured.
What Do These Findings Mean?
These findings show that active case finding for tuberculosis delivered through a mobile HIV testing service is feasible and has a high uptake, yield and treatment success in deprived communities with a high prevalence of HIV and tuberculosis. The findings also highlight the challenges faced by mobile population-based services such as losses between tuberculosis diagnosis and treatment, which were greatest for smear-negative/culture-positive people who were more difficult to contact than smear-positive people because of the greater time lag between sputum collection and diagnosis. Because the study was done in a single city, these findings need to be confirmed in other settings—the yield of active tuberculosis case finding reported here, for example, is not likely to be generalizable to countries that rely on sputum smears for tuberculosis diagnosis. Finally, given that the incremental cost per case treated in this study is 3-fold higher than the incremental cost per case treated under passive case detection in South Africa, further studies are needed to determine the cost-effectiveness and affordability of population-based tuberculosis screening.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001281.
The World Health Organization provides information on all aspects of tuberculosis, including information on tuberculosis and HIV, and on the Three I?s for HIV/TB (some information is in several languages); details of a 2011 meeting on the development of guidelines on screening for active tuberculosis are available
The Stop TB partnership is working towards tuberculosis elimination; patient stories about tuberculosis/HIV coinfection are available
The US Centers for Disease Control and Prevention has information about tuberculosis, about tuberculosis and HIV co-infection, and about the diagnosis of tuberculosis disease
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
The Tuberculosis Survival Project, which aims to raise awareness of tuberculosis and provide support for people with tuberculosis, provides personal stories about treatment for tuberculosis; the Tuberculosis Vaccine Initiative also provides personal stories about dealing with tuberculosis
doi:10.1371/journal.pmed.1001281
PMCID: PMC3413719  PMID: 22879816
2.  Serological Testing Versus Other Strategies for Diagnosis of Active Tuberculosis in India: A Cost-Effectiveness Analysis 
PLoS Medicine  2011;8(8):e1001074.
This cost-effectiveness study shows that sputum smear microscopy is the most cost-effective test for active tuberculosis (TB) in India, and liquid culture plus microscopy is more cost-effective for TB diagnosis than serological tests.
Background
Undiagnosed and misdiagnosed tuberculosis (TB) drives the epidemic in India. Serological (antibody detection) TB tests are not recommended by any agency, but widely used in many countries, including the Indian private sector. The cost and impact of using serology compared with other diagnostic techniques is unknown.
Methods and Findings
Taking a patient cohort conservatively equal to the annual number of serological tests done in India (1.5 million adults suspected of having active TB), we used decision analysis to estimate costs and effectiveness of sputum smear microscopy (US$3.62 for two smears), microscopy plus automated liquid culture (mycobacterium growth indicator tube [MGIT], US$20/test), and serological testing (anda-tb ELISA, US$20/test). Data on test accuracy and costs were obtained from published literature. We adopted the perspective of the Indian TB control sector and an analysis frame of 1 year. Our primary outcome was the incremental cost per disability-adjusted life year (DALY) averted. We performed one-way sensitivity analysis on all model parameters, with multiway sensitivity analysis on variables to which the model was most sensitive.
If used instead of sputum microscopy, serology generated an estimated 14,000 more TB diagnoses, but also 121,000 more false-positive diagnoses, 102,000 fewer DALYs averted, and 32,000 more secondary TB cases than microscopy, at approximately four times the incremental cost (US$47.5 million versus US$11.9 million). When added to high-quality sputum smears, MGIT culture was estimated to avert 130,000 incremental DALYs at an incremental cost of US$213 per DALY averted. Serology was dominated by (i.e., more costly and less effective than) MGIT culture and remained less economically favorable than sputum smear or TB culture in one-way and multiway sensitivity analyses.
Conclusions
In India, sputum smear microscopy remains the most cost-effective diagnostic test available for active TB; efforts to increase access to quality-assured microscopy should take priority. In areas where high-quality microscopy exists and resources are sufficient, MGIT culture is more cost-effective than serology as an additional diagnostic test for TB. These data informed a recently published World Health Organization policy statement against serological tests.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Every year, about 2 million people develop tuberculosis in India—a fifth of the global incidence of this highly contagious bacterial infection. Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is spread in airborne droplets when people with the disease cough or sneeze and usually infects the lungs although it can also infect other organs. The characteristic symptoms of tuberculosis are a persistent cough, weight loss, and night sweats. Diagnostic tests for tuberculosis include sputum smear microscopy (microscopic analysis of mucus brought up from the lungs by coughing), culture (growth) of M. tuberculosis from sputum samples in liquid media (using, for example, a commercial product called the mycobacteria growth indicator tube or MGIT), and nucleic acid amplification tests (which detect the bacterium's genome in patient samples) such as the Xpert MTB/RIF system. Tuberculosis can usually be cured by taking several powerful antibiotics daily for at least 6 months.
Why Was This Study Done?
In India, as elsewhere, undiagnosed and misdiagnosed tuberculosis drives the tuberculosis epidemic by increasing the transmission of M. tuberculosis. Unfortunately, sputum smear microscopy, the current mainstay of tuberculosis diagnosis worldwide, detects only half of tuberculosis cases, mycobacterial culture can take weeks to provide a diagnosis, and rapid techniques such as nucleic acid amplification require infrastructure that is often not available in developing countries. Consequently, in India and other developing countries, serological tests are widely used for the diagnosis of tuberculosis. Serological tests detect antibodies against M. tuberculosis in the blood (antibodies are proteins made by the immune system in response to infections). Serological tests are fast and simple to perform, but they are not recommended for clinical use, and the available evidence suggests that they do not diagnose tuberculosis accurately. Even so, and in the absence of information about the cost and impact (cost-effectiveness) of serological testing, about 1.5 million serological tests for tuberculosis are conducted every year in India at a cost of more than US$15 million. Here, the researchers analyze the cost-effectiveness of serological tests compared to other diagnostic tests from the perspective of tuberculosis control in India.
What Did the Researchers Do and Find?
The researchers used “decision analysis” to estimate the cost-effectiveness of sputum smear microscopy, microscopy plus liquid culture using the MGIT system, and serological testing using the widely used anda-tb ELISA commercial test in a hypothetical group of 1.5 million people suspected of having tuberculosis. Decision analysis formally assesses the decision-making process by using models that evaluate outcomes under different scenarios. By feeding data on the costs and accuracy of different diagnostic tests into their decision-analysis model, the researchers estimate that, over a year, serology would generate 14,000 more tuberculosis diagnoses than sputum microscopy. However, it would also generate 121,000 more false-positive diagnoses and 32,000 more tuberculosis transmissions to other people (secondary transmissions), and avert 102,000 fewer disability-adjusted life years (DALYs; a DALY is a year of healthy life lost because of premature death or disability) at four times the incremental cost of sputum microscopy. MGIT culture added to sputum smear microscopy would avert 130,000 DALYs at an incremental cost of US$213 per DALY averted. Finally, sensitivity analyses (reruns of the decision-analysis model using different values for test costs and accuracy) identified no scenario in which serology was either less costly or more effective than sputum smear microscopy alone or in which serology plus sputum microscopy was more cost-effective than MGIT culture plus sputum microscopy.
What Do These Findings Mean?
These findings identify sputum smear microscopy as the most cost-effective existing diagnostic test for tuberculosis in India. Moreover, they suggest that in areas where high-quality microscopy is available, resources are sufficient, and infrastructure to effectively use culture exists, the addition of MGIT culture to sputum smear microscopy would be more cost-effective than the addition of serology. Importantly, these findings suggest that, if used as an initial test for tuberculosis in India, serology would result in more DALYs, more secondary infections, and more false-positive diagnoses than sputum smear microscopy while increasing per-patient costs to the Indian tuberculosis control sector. Given these findings and the results of a recent updated systematic review on the accuracy of serological tests, the World Health Organization's Strategic and Technical Advisory Group for Tuberculosis recently advised against the use of currently available serological tests for the diagnosis of tuberculosis. The WHO negative policy against serological tests must now be implemented in India.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001074.
Details of the recent systematic review of serological tests for tuberculosis diagnosis are available in a PLoS Medicine Research Article by Steingart et al.
The World Health Organization provides information on all aspects of tuberculosis, including tuberculosis diagnostics and the Stop TB Partnership (some information is in several languages); its Strategic and Technical Advisory Group for Tuberculosis recommendations on tuberculosis diagnosis are available
The Evidence-based TB Diagnosis Web site by the Stop TB Partnership's New Diagnostics Working Group provides evidence syntheses on various TB tests, along with guidelines, resources, and training materials
The US Centers for Disease Control and Prevention has information about tuberculosis, including information on the diagnosis of tuberculosis disease
The US National Institute of Allergy and Infectious Diseases also has information on all aspects of tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001074
PMCID: PMC3153451  PMID: 21857810
3.  Screening for HIV-Associated Tuberculosis and Rifampicin Resistance before Antiretroviral Therapy Using the Xpert MTB/RIF Assay: A Prospective Study 
PLoS Medicine  2011;8(7):e1001067.
In a prospective study, Stephen Lawn and colleagues find that pre-ART screening with Xpert MTB/RIF increased tuberculosis case detection by 45% compared to smear microscopy in HIV-positive patients at high risk of TB risk. AE competing interests must also pull through to the proof. “The Academic Editor, Madhukar Pai, declares that he consults for the Bill & Melinda Gates Foundation (BMGF). The BMGF supported FIND which was involved in the development of the Xpert MTB/RIF assay. He also co-chairs the Stop TB Partnership's New Diagnostics Working Group that was involved in the WHO endorsement of the Xpert assay.” Linked: Scott pmed.1001061; Evans pmed.1001064; Dowdy pmed.1001063
Background
The World Health Organization has endorsed the Xpert MTB/RIF assay for investigation of patients suspected of having tuberculosis (TB). However, its utility for routine TB screening and detection of rifampicin resistance among HIV-infected patients with advanced immunodeficiency enrolling in antiretroviral therapy (ART) services is unknown.
Methods and Findings
Consecutive adult HIV-infected patients with no current TB diagnosis enrolling in an ART clinic in a South African township were recruited regardless of symptoms. They were clinically characterised and invited to provide two sputum samples at a single visit. The accuracy of the Xpert MTB/RIF assay for diagnosing TB and drug resistance was assessed in comparison with other tests, including fluorescence smear microscopy and automated liquid culture (gold standard) and drug susceptibility testing. Of 515 patients enrolled, 468 patients (median CD4 cell count, 171 cells/µl; interquartile range, 102–236) produced at least one sputum sample, yielding complete sets of results from 839 samples. Mycobacterium tuberculosis was cultured from 81 patients (TB prevalence, 17.3%). The overall sensitivity of the Xpert MTB/RIF assay for culture-positive TB was 73.3% (specificity, 99.2%) compared to 28.0% (specificity, 100%) using smear microscopy. All smear-positive, culture-positive disease was detected by Xpert MTB/RIF from a single sample (sensitivity, 100%), whereas the sensitivity for smear-negative, culture-positive TB was 43.4% from one sputum sample and 62.3% from two samples. Xpert correctly identified rifampicin resistance in all four cases of multidrug-resistant TB but incorrectly identified resistance in three other patients whose disease was confirmed to be drug sensitive by gene sequencing (specificity, 94.1%; positive predictive value, 57%).
Conclusions
In this population of individuals at high risk of TB, intensive screening using the Xpert MTB/RIF assay increased case detection by 45% compared with smear microscopy, strongly supporting replacement of microscopy for this indication. However, despite the ability of the assay to rapidly detect rifampicin-resistant disease, the specificity for drug-resistant TB was sub-optimal.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis (TB)—a contagious bacterial infection that mainly affects the lungs—is a leading cause of illness and death among people who are infected with HIV, the virus that causes AIDS by destroying the immune system, which leaves infected individuals susceptible to other infections. TB is caused by Mycobacterium tuberculosis, which is spread in airborne droplets when people with the disease cough or sneeze. Its symptoms include a persistent cough, weight loss, and night sweats. Diagnostic tests for TB include chest X-rays, sputum smear analysis (microscopic examination of mucus coughed up from the lungs for M. tuberculosis bacilli), and mycobacterial liquid culture (the growth of M. tuberculosis from sputum and determination of its drug sensitivity). TB can be cured by taking several drugs daily for six months, although the recent emergence of multidrug-resistant TB (MDR-TB) is making the disease increasingly hard to treat.
Why Was This Study Done?
TB is a major problem in clinics that provide antiretroviral therapy (ART) for HIV-positive people in resource-limited settings. Not only is it a major cause of sickness and mortality in those affected by it, but TB (especially MDR-TB) can also spread to other patients attending the same clinic for health services. Rapid diagnosis and appropriate treatment are very important to reduce these risks. Unfortunately, sputum smear analysis—the mainstay of TB diagnosis in resource-limited settings—only detects about a fifth of TB cases when used as a screening tool before initiating ART. Chest X-rays are costly and don't always detect TB, and liquid culture—the gold standard method for TB diagnosis—is costly, technically difficult, and slow. Consequently, the World Health Organization (WHO) recently endorsed a new test for the investigation of patients suspected of having TB, especially in regions where HIV infection and MDR-TB are common. Xpert MTB/RIF is an automated DNA test that detects M. tuberculosis and DNA differences that make the bacteria resistant to the drug rifampicin (an indicator of MDR-TB) within 2 hours. In this study, the researchers investigate whether Xpert MTB/RIF could be used as a routine screening test to increase TB detection among HIV-positive people initiating ART.
What Did the Researchers Do and Find?
The researchers collected sputum from HIV-infected adults with no current TB diagnosis enrolling at an ART clinic in a South African township where HIV infection and TB are both common. They then compared the diagnostic accuracy of Xpert MTB/RIF (performed at a centralized laboratory) with that of several other tests, including liquid culture (the reference test). Nearly a fifth of the patients had culture-positive TB. Xpert MTB/RIF identified three-quarters of these patients (a sensitivity of 73.3%). By contrast, the sensitivity of smear microscopy was 28%. The new test's specificity (the proportion of patients with a negative Xpert MTB/RIF result among patients without TB) was 99.2%. That is, Xpert MTB/RIF had a low false-positive rate. Notably, Xpert MTB/RIF detected all cases of smear-positive, culture-positive TB but only 43.4% of smear-negative, culture-positive cases from a single sputum sample; it detected 62.3% of such cases when two sputum samples were analyzed. Finally, Xpert MTB/RIF correctly identified rifampicin resistance in all four patients who had MDR-TB but incorrectly identified resistance in three patients with drug-sensitive TB.
What Do These Findings Mean?
In this population of HIV-positive patients with a high TB risk, pre-ART screening with Xpert MTB/RIF increased case detection by 45% compared to smear microscopy, a finding that needs confirming in other settings. Importantly, Xpert MTB/RIF reduced the delay in diagnosis of TB from more than 20 days to two days. This delay would be reduced further by doing the assay at ART clinics rather than at a centralized testing facility, but the diagnostic accuracy of point-of-care testing needs evaluating. Overall, these findings (and those of an accompanying article by Scott et al. that examines the performance of Xpert MTB/RIF in an area where HIV infection is common) support the replacement of smear microscopy with Xpert MTB/RIF for pre-ART TB screening (provided misdiagnosis of rifampicin resistance can be reduced). These findings also suggest that routine screening with Xpert MTB/RIF could reduce the risk of MDR-TB outbreaks in HIV care and treatment settings and improve outcomes for HIV-positive patients with MDR-TB who currently often die before a diagnosis of TB can be made.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001056.
This study is further discussed in a PLoS Medicine Perspective by Carlton Evans; a related PLoS Medicine Research Article by Scott et al. is also available
WHO provides information (in several languages) on all aspects of tuberculosis, including general information on tuberculosis diagnostics and specific information on the Xpert MTB/RIF test; further information about WHO's endorsement of Xpert MTB/RIF is included in a recent Strategic and Technical Advisory Group for Tuberculosis report
WHO also provides information about tuberculosis and HIV
The US National Institute of Allergy and Infectious Diseases has detailed information on tuberculosis and HIV/AIDS
The US Centers for Disease Control and Prevention also has information about tuberculosis, including information on the diagnosis of and on tuberculosis and HIV co-infection
Information is available from Avert, an international AIDS charity, on many aspects of HIV/AIDS, including information on HIV-related tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001067
PMCID: PMC3144215  PMID: 21818180
4.  LED Fluorescence Microscopy for the Diagnosis of Pulmonary Tuberculosis: A Multi-Country Cross-Sectional Evaluation 
PLoS Medicine  2011;8(7):e1001057.
This study, nested within a clinical trial, by Luis Cuevas and colleagues finds that LED-FM microscopy has higher sensitivity but lower specificity than Zn microscopy for detecting tuberculosis in sputum samples.
Background
The diagnosis of tuberculosis (TB) in resource-limited settings relies on Ziehl-Neelsen (ZN) smear microscopy. LED fluorescence microscopy (LED-FM) has many potential advantages over ZN smear microscopy, but requires evaluation in the field. The aim of this study was to assess the sensitivity/specificity of LED-FM for the diagnosis of pulmonary TB and whether its performance varies with the timing of specimen collection.
Methods and Findings
Adults with cough ≥2 wk were enrolled consecutively in Ethiopia, Nepal, Nigeria, and Yemen. Sputum specimens were examined by ZN smear microscopy and LED-FM and compared with culture as the reference standard. Specimens were collected using a spot-morning-spot (SMS) or spot-spot-morning (SSM) scheme to explore whether the collection of the first two smears at the health care facility (i.e., “on the spot”) the first day of consultation followed by a morning sample the next day (SSM) would identify similar numbers of smear-positive patients as smears collected via the SMS scheme (i.e., one on-the-spot-smear the first day, followed by a morning specimen collected at home and a second on-the-spot sample the second day). In total, 529 (21.6%) culture-positive and 1,826 (74.6%) culture-negative patients were enrolled, of which 1,156 (49%) submitted SSM specimens and 1,199 (51%) submitted SMS specimens. Single LED-FM smears had higher sensitivity but lower specificity than single ZN smears. Using two LED-FM or two ZN smears per patient was 72.8% (385/529, 95% CI 68.8%–76.5%) and 65.8% (348/529, 95% CI 61.6%–69.8%) sensitive (p<0.001) and 90.9% (1,660/1,826, 95% CI 89.5%–92.2%) and 98% (1,790/1,826, 95% CI 97.3%–98.6%) specific (p<0.001). Using three LED-FM or three ZN smears per patient was 77% (408/529, 95% CI 73.3%–80.6%) and 70.5% (373/529, 95% CI 66.4%–74.4%, p<0.001) sensitive and 88.1% (95% CI 86.5%–89.6%) and 96.5% (95% CI 96.8%–98.2%, p<0.001) specific. The sensitivity/specificity of ZN smear microscopy and LED-FM did not vary between SMS and SSM.
Conclusions
LED-FM had higher sensitivity but, in this study, lower specificity than ZN smear microscopy for diagnosis of pulmonary TB. Performance was independent of the scheme used for collecting specimens. The introduction of LED-FM needs to be accompanied by appropriate training, quality management, and monitoring of performance in the field.
Trial Registration
Current Controlled Trials ISRCTN53339491
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis is a global public health problem. Every year, about 1.7 million people die from this contagious bacterial infection, and about 9 million new cases occur, mainly in low- and middle-income countries. Mycobacterium tuberculosis, which causes tuberculosis, is spread in airborne droplets when people with the disease cough or sneeze, and usually infects the lungs (pulmonary tuberculosis). Symptoms of tuberculosis include a persistent cough, weight loss, and night sweats. Because tuberculosis is easily transmitted and potentially deadly, it is important that it is diagnosed quickly and accurately and immediately treated. The “gold standard” diagnostic test for tuberculosis is mycobacterial culture (in liquid or solid medium), in which laboratory technicians try to grow M. tuberculosis from sputum (mucus brought up from the lungs by coughing). However, this test is expensive, so most patients suspected of having pulmonary tuberculosis in resource-limited countries are investigated using sputum smear microscopy. In this cheaper but less sensitive test, sputum samples are “smeared” onto microscope slides, stained with Ziehl-Neelsen (ZN) dye, and then examined with a microscope for the presence of M. tuberculosis.
Why Was This Study Done?
With smear microscopy, multiple samples have to be examined to increase the test's sensitivity (the proportion of patients with culture-positive tuberculosis that the test detects). Because each smear examination takes up to 10 minutes, tuberculosis diagnosis with ZN smear microscopy creates a large laboratory workload. A variant form of smear microscopy—light-emitting-diode fluorescence microscopy (LED-FM)—could reduce this workload. With LED-FM, smears stained with a fluorescent dye can be examined in a quarter of the time it takes to examine ZN smears. In this study, the researchers evaluate the sensitivity and specificity (the proportion of people with a negative smear among people without tuberculosis; a high specificity indicates a low false-positive rate) of LED-FM using samples collected in a trial undertaken in four resource-limited countries (Ethiopia, Nepal, Nigeria, and Yemen) to investigate two schemes for sputum sample collection. In the spot-morning-spot (SMS) scheme, patients provide an on-the-spot specimen at their initial consultation, a specimen collected at home the next morning, and a second on-the-spot sample when they deliver their morning specimen. In the spot-spot-morning (SSM) scheme, patients provide two on-the-spot samples during their first clinic visit and a sample collected at home the next morning.
What Did the Researchers Do and Find?
In the main trial, the researchers collected sputum samples using the SMS or SSM scheme from 6,627 patients with a cough lasting more than two weeks. For their investigation of LED-FM, they examined nearly 2,400 samples (half SSM and half SMS specimens, about a quarter of which were tuberculosis culture-positive) with both ZN smear microscopy and LED-FM and determined the sensitivity and specificity of both tests—with one, two, or three sputum samples per patient—relative to mycobacterial solid culture. Single LED-FM smears had higher sensitivity but lower specificity than single ZN smears. The sensitivities of two LED-FM and two ZN smears were 72.8% and 65.8%, respectively; the specificities of these tests were 90.9% and 98.0%. The sensitivities of three LED-FM and three ZN smears were 77% and 70.5%, respectively; the specificities of these tests were 88.1% and 96.5%. The sensitivity and specificity of both tests was similar for samples collected using the SMS and the SSM schemes.
What Do These Findings Mean?
These findings show that in the resource-limited countries included in this trial, LED-FM has a higher sensitivity but lower specificity than ZN smear microscopy. The researchers calculate that in this study the accuracy of three LED-FM examinations was 85% (2,017 out of 2,355 patients were correctly classified as infected or uninfected), whereas the accuracy of three ZN smears was 91.8%. Thus, although LED-FM should identify more people with tuberculosis than ZN smear microscopy, because of its lower specificity, its use might also lead to more people without tuberculosis being needlessly treated for the disease. Nevertheless, provided that the introduction of LED-FM is accompanied by appropriate training and performance monitoring, LED-FM is an attractive potential tool for the laboratory diagnosis of tuberculosis that, together with a move towards the collection of two on-the-spot smears in a single clinic visit, could ensure that poor patients have access to timely tuberculosis diagnosis and prompt treatment.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001057.
Details of the parent trial in which the samples used in this study were collected are available in a PLoS Medicine Research Article by Cuevas et al.
The World Health Organization provides information on all aspects of tuberculosis, including information on tuberculosis diagnostics; recent WHO policy statements on diagnosis of tuberculosis are available; the Stop TB Partnership provides information on global tuberculosis control (some information in several languages)
The US Centers for Disease Control and Prevention has information about tuberculosis, including information on the diagnosis of tuberculosis disease
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
A new Web site dedicated to the discussion and optimization of smear microscopy has recently been launched
doi:10.1371/journal.pmed.1001057
PMCID: PMC3134458  PMID: 21765809
5.  Rapid Diagnosis of Tuberculosis with the Xpert MTB/RIF Assay in High Burden Countries: A Cost-Effectiveness Analysis 
PLoS Medicine  2011;8(11):e1001120.
A cost-effectiveness study by Frank Cobelens and colleagues reveals that Xpert MTB/RIF is a cost-effective method of tuberculosis diagnosis that is suitable for use in low- and middle-income settings.
Background
Xpert MTB/RIF (Xpert) is a promising new rapid diagnostic technology for tuberculosis (TB) that has characteristics that suggest large-scale roll-out. However, because the test is expensive, there are concerns among TB program managers and policy makers regarding its affordability for low- and middle-income settings.
Methods and Findings
We estimate the impact of the introduction of Xpert on the costs and cost-effectiveness of TB care using decision analytic modelling, comparing the introduction of Xpert to a base case of smear microscopy and clinical diagnosis in India, South Africa, and Uganda. The introduction of Xpert increases TB case finding in all three settings; from 72%–85% to 95%–99% of the cohort of individuals with suspected TB, compared to the base case. Diagnostic costs (including the costs of testing all individuals with suspected TB) also increase: from US$28–US$49 to US$133–US$146 and US$137–US$151 per TB case detected when Xpert is used “in addition to” and “as a replacement of” smear microscopy, respectively. The incremental cost effectiveness ratios (ICERs) for using Xpert “in addition to” smear microscopy, compared to the base case, range from US$41–$110 per disability adjusted life year (DALY) averted. Likewise the ICERS for using Xpert “as a replacement of” smear microscopy range from US$52–$138 per DALY averted. These ICERs are below the World Health Organization (WHO) willingness to pay threshold.
Conclusions
Our results suggest that Xpert is a cost-effective method of TB diagnosis, compared to a base case of smear microscopy and clinical diagnosis of smear-negative TB in low- and middle-income settings where, with its ability to substantially increase case finding, it has important potential for improving TB diagnosis and control. The extent of cost-effectiveness gain to TB programmes from deploying Xpert is primarily dependent on current TB diagnostic practices. Further work is required during scale-up to validate these findings.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis (TB) is a bacterial disease that infects one-third of the world's population. The disease is caused by Mycobacterium tuberculosis, a bacterium that most commonly infects the lungs (known as pulmonary TB) and is transmitted from person to person when an infected individual coughs, sneezes, or talks. The symptoms of TB include chest pain, weight loss, fever, and a persistent cough that sometimes contains blood. Only 5%–10% of people who are infected with TB become sick or infectious, but people with weakened immune systems, such as individuals who are HIV-positive, are more likely to develop the disease. TB is estimated to have killed 1.7 million people in 2009 and is currently the leading cause of death among people infected with HIV.
Why Was This Study Done?
Although TB can be treated with a six-month course of antibiotics, effectively diagnosing TB is not always straightforward and drug resistance is becoming an increasing problem. One of the most common and simple methods to diagnose TB is a technique called sputum smear microscopy, which involves examining matter from the lungs under a microscope for the presence of TB-causing bacteria. However, despite being cheap and relatively simple, the test does not always detect active TB (smear-negative) and cannot determine whether the TB-causing bacteria are resistant to antibiotics. The World Health Organization has recently endorsed a new rapid test, called Xpert MTB/RIF (referred to as Xpert), for the initial diagnosis of TB. The test uses DNA amplification methods to reliably and quickly detect TB and whether infecting bacteria are resistant to the antibiotic rifampicin. The new test is expensive so there are concerns that the test might not be cost-effective in low- and middle-income countries.
What Did the Researchers Do and Find?
The researchers used a technique called modeling to simulate the outcome of 10,000 individuals with suspected TB as they went through a hypothetical diagnostic and treatment pathway. The model compared the costs associated with the introduction of Xpert to a base case for two different scenarios. In the base case all individuals with suspected TB had two sputum smear microscopy examinations followed by clinical diagnosis if they were smear-negative. For the different scenarios Xpert was either used in addition to the two sputum smear microscopy examinations (if the patient was smear-negative) or Xpert was used as a replacement for sputum smear microscopy for all patients. Different input parameters, based on country-specific estimates, were applied so that the model reflected the implementation of Xpert in India, South Africa, and Uganda.
In the researcher's model the introduction of Xpert increased the proportion of TB-infected patients who were correctly diagnosed with TB in any of the settings. However, the cost per TB case detected increased by approximately US$100 in both scenarios. Although the cost of detection increased significantly, the cost of treatment increased only moderately because the number of false-positive cases was reduced. For example, the percentage of treatment costs spent on false-positive diagnoses in India was predicted to fall from 22% to 4% when Xpert was used to replace sputum smear microscopy. The model was used to calculate incremental cost effectiveness ratios (ICERs—the additional cost of each disability-adjusted life year [DALY] averted) for the different scenarios of Xpert implementation in the different settings. In comparison to the base case, introducing Xpert in addition to sputum smear microscopy produced ICERs ranging from US$41 to US$110 per DALY averted, while introducing Xpert instead of sputum smear microscopy yielded ICERs ranging from US$52 to US$138 per DALY averted.
What Do These Findings Mean?
The findings suggest that the implementation of Xpert in addition to, or instead of, sputum smear microscopy will be cost-effective in low- and middle-income countries. The calculated ICERs are below the World Health Organization's “willingness to pay threshold” for all settings. That is the incremental cost of each DALY averted by introduction of Xpert is below the gross domestic product per capita for each country ($1,134 for India, $5,786 South Africa, and $490 for Uganda in 2010). However, the authors note that achieving ICERs below the “willingness to pay threshold” does not necessarily mean that countries have the resources to implement the test. The researchers also note that there are limitations to their study; additional unknown costs associated with the scale-up of Xpert and some parameters, such as patient costs, were not included in the model. Although the model strongly suggests that Xpert will be cost-effective, the researchers caution that initial roll-out of Xpert should be carefully monitored and evaluated before full scale-up.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001120.
The World Health Organization provides information on all aspects of tuberculosis, including tuberculosis diagnostics and the Stop TB Partnership (some information is in several languages)
The US Centers for Disease Control and Prevention has information about tuberculosis, including information on the diagnosis of tuberculosis disease
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001120
PMCID: PMC3210757  PMID: 22087078
6.  Impact of Xpert MTB/RIF for TB Diagnosis in a Primary Care Clinic with High TB and HIV Prevalence in South Africa: A Pragmatic Randomised Trial 
PLoS Medicine  2014;11(11):e1001760.
Helen Cox and colleagues investigate the impact Xpert MTB/RIF for diagnosing patients with presumptive tuberculosis in a large primary care clinic in Khayelitsha, Cape Town.
Please see later in the article for the Editors' Summary
Background
Xpert MTB/RIF is approved for use in tuberculosis (TB) and rifampicin-resistance diagnosis. However, data are limited on the impact of Xpert under routine conditions in settings with high TB burden.
Methods and Findings
A pragmatic prospective cluster-randomised trial of Xpert for all individuals with presumptive (symptomatic) TB compared to the routine diagnostic algorithm of sputum microscopy and limited use of culture was conducted in a large TB/HIV primary care clinic. The primary outcome was the proportion of bacteriologically confirmed TB cases not initiating TB treatment by 3 mo after presentation. Secondary outcomes included time to TB treatment and mortality. Unblinded randomisation occurred on a weekly basis. Xpert and smear microscopy were performed on site. Analysis was both by intention to treat (ITT) and per protocol.
Between 7 September 2010 and 28 October 2011, 1,985 participants were assigned to the Xpert (n = 982) and routine (n = 1,003) diagnostic algorithms (ITT analysis); 882 received Xpert and 1,063 routine (per protocol analysis). 13% (32/257) of individuals with bacteriologically confirmed TB (smear, culture, or Xpert) did not initiate treatment by 3 mo after presentation in the Xpert arm, compared to 25% (41/167) in the routine arm (ITT analysis, risk ratio 0.51, 95% CI 0.33–0.77, p = 0.0052).
The yield of bacteriologically confirmed TB cases among patients with presumptive TB was 17% (167/1,003) with routine diagnosis and 26% (257/982) with Xpert diagnosis (ITT analysis, risk ratio 1.57, 95% CI 1.32–1.87, p<0.001). This difference in diagnosis rates resulted in a higher rate of treatment initiation in the Xpert arm: 23% (229/1,003) and 28% (277/982) in the routine and Xpert arms, respectively (ITT analysis, risk ratio 1.24, 95% CI 1.06–1.44, p = 0.013). Time to treatment initiation was improved overall (ITT analysis, hazard ratio 0.76, 95% CI 0.63–0.92, p = 0.005) and among HIV-infected participants (ITT analysis, hazard ratio 0.67, 95% CI 0.53–0.85, p = 0.001). There was no difference in 6-mo mortality with Xpert versus routine diagnosis. Study limitations included incorrect intervention allocation for a high proportion of participants and that the study was conducted in a single clinic.
Conclusions
These data suggest that in this routine primary care setting, use of Xpert to diagnose TB increased the number of individuals with bacteriologically confirmed TB who were treated by 3 mo and reduced time to treatment initiation, particularly among HIV-infected participants.
Trial registration
Pan African Clinical Trials Registry PACTR201010000255244
Please see later in the article for the Editors' Summary
Editors' Summary
Background
In 2012, about 8.6 million people developed active tuberculosis (TB)—a contagious mycobacterial disease that usually affects the lungs—and at least 1.3 million people died from the disease. Most of these deaths were in low- and middle-income countries, and a fifth were in HIV-positive individuals, who are particularly susceptible to TB. Mycobacterium tuberculosis, the bacterium that causes TB, is spread in airborne droplets when people with active disease cough or sneeze. The characteristic symptoms of TB include a cough, weight loss, and night sweats. Diagnostic tests for TB include microscopic examination of sputum (mucus coughed up from the lungs), growth (culture) of M. tuberculosis from sputum, and molecular tests (for example, the automated Xpert MTB/RIF test) that rapidly and accurately detect M. tuberculosis in sputum and determine its antibiotic resistance. TB can be cured by taking several antibiotics daily for at least six months, although the emergence of multidrug-resistant TB is making the disease harder to treat.
Why Was This Study Done?
To improve TB control, active disease needs to be diagnosed and treated quickly. However, sputum microscopy, the mainstay of TB diagnosis in many high-burden settings, fails to identify up to half of infected people, and mycobacterial culture (the “gold standard” of TB diagnosis) is slow and often unavailable in resource-limited settings. In late 2010, the World Health Organization recommended the routine use of the Xpert MTB/RIF test (Xpert) for TB diagnosis, and several low- and middle-income countries are now scaling up access to Xpert in their national TB control programs. But although Xpert performs well in ideal conditions, little is known about the impact of its implementation in routine (real-life) settings. In this pragmatic cluster-randomized trial, the researchers assess the health impacts of Xpert in a large TB/HIV primary health care clinic in South Africa, an upper-middle-income country that began to scale up access to Xpert for individuals showing symptoms of TB (individuals with presumptive TB) in 2011. A pragmatic trial asks whether an intervention works under real-life conditions; a cluster-randomized trial randomly assigns groups of people to receive alternative interventions and compares outcomes in the differently treated “clusters.”
What Did the Researchers Do and Find?
The researchers assigned everyone with presumptive TB attending a TB/HIV primary health care clinic in Cape Town to receive either Xpert for TB diagnosis or routine sputum microscopy and limited culture. Specifically, Xpert was requested on the routine laboratory request forms for individuals attending the clinic during randomly designated Xpert weeks but not during randomly designated routine testing weeks. During the 51-week trial, 982 individuals were assigned to the Xpert arm, and 1,003 were assigned to the routine testing arm, but because clinic staff sometimes failed to request Xpert during Xpert weeks, only 882 participants in the Xpert arm received the intervention. In an “intention to treat” analysis (an analysis that considers the outcomes of all the participants in a trial whether or not they received their assigned intervention), 13% of bacteriologically confirmed TB cases in the Xpert arm did not initiate TB treatment by three months after enrollment (the trial's primary outcome) compared to 25% in the routine testing arm. The proportion of participants with microbiologically confirmed TB and the proportion initiating TB treatment were higher in the Xpert arm than in the routine testing arm. Finally, the time to treatment initiation was lower in the Xpert arm than in the routine testing arm, particularly among HIV-infected participants.
What Do These Findings Mean?
These findings show that, in this primary health care setting, the provision of Xpert for TB diagnosis in individuals with presumptive TB provided benefits over testing that relied primarily on sputum microscopy. Notably, these benefits were seen even though a substantial proportion of individuals assigned to the Xpert intervention did not actually receive an Xpert test. The pragmatic nature of this trial, which aimed to minimize clinic disruption, and other aspects of the trial design may limit the accuracy and generalizability of these findings. Moreover, further studies are needed to discover whether the use of Xpert in real-life settings reduces the burden of TB illness and death over the long term. Nevertheless, these findings suggest that the implementation of Xpert has the potential to improve the outcomes of TB control programs and may also improve outcomes for individuals.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001760.
The World Health Organization provides information (in several languages) on all aspects of tuberculosis, including general information on tuberculosis diagnostics and specific information on the roll-out of the Xpert MTB/RIF test; further information about the World Health Organization's endorsement of Xpert MTB/RIF is included in a Strategic and Technical Advisory Group for Tuberculosis report; the “Global Tuberculosis Report 2013” provides information about tuberculosis around the world, including in South Africa
The Stop TB Partnership is working towards tuberculosis elimination and provides patient stories about tuberculosis (in English and Spanish); the Tuberculosis Vaccine Initiative (a not-for-profit organization) also provides personal stories about tuberculosis
The US Centers for Disease Control and Prevention has information about tuberculosis and its diagnosis (in English and Spanish)
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
The South African National Tuberculosis Management Guidelines 2014 are available
The Foundation for Innovative New Diagnostics, a not-for-profit organization that helps to develop and introduce new diagnostic tests for tuberculosis, malaria, and neglected tropical diseases, has detailed information about the Xpert MTB/RIF test
More information about TB, HIV, and drug-resistant TB treatment in Khayelitsha, Cape Town, South Africa are provided by Médecins sans Frontières, South Africa
doi:10.1371/journal.pmed.1001760
PMCID: PMC4244039  PMID: 25423041
7.  Comparison of Xpert MTB/RIF with Other Nucleic Acid Technologies for Diagnosing Pulmonary Tuberculosis in a High HIV Prevalence Setting: A Prospective Study 
PLoS Medicine  2011;8(7):e1001061.
In this prospective, real-world cohort study nested within a national screening program for tuberculosis, Lesley Scott and colleagues compare the performance of Xpert MTB/RIF on a single sputum sample with different TB sputum detection technologies.
Background
The Xpert MTB/RIF (Cepheid) non-laboratory-based molecular assay has potential to improve the diagnosis of tuberculosis (TB), especially in HIV-infected populations, through increased sensitivity, reduced turnaround time (2 h), and immediate identification of rifampicin (RIF) resistance. In a prospective clinical validation study we compared the performance of Xpert MTB/RIF, MTBDRplus (Hain Lifescience), LightCycler Mycobacterium Detection (LCTB) (Roche), with acid fast bacilli (AFB) smear microscopy and liquid culture on a single sputum specimen.
Methods and Findings
Consecutive adults with suspected TB attending a primary health care clinic in Johannesburg, South Africa, were prospectively enrolled and evaluated for TB according to the guidelines of the National TB Control Programme, including assessment for smear-negative TB by chest X-ray, clinical evaluation, and HIV testing. A single sputum sample underwent routine decontamination, AFB smear microscopy, liquid culture, and phenotypic drug susceptibility testing. Residual sample was batched for molecular testing. For the 311 participants, the HIV prevalence was 70% (n = 215), with 120 (38.5%) culture-positive TB cases. Compared to liquid culture, the sensitivities of all the test methodologies, determined with a limited and potentially underpowered sample size (n = 177), were 59% (47%–71%) for smear microscopy, 76% (64%–85%) for MTBDRplus, 76% (64%–85%) for LCTB, and 86% (76%–93%) for Xpert MTB/RIF, with specificities all >97%. Among HIV+ individuals, the sensitivity of the Xpert MTB/RIF test was 84% (69%–93%), while the other molecular tests had sensitivities reduced by 6%. TB detection among smear-negative, culture-positive samples was 28% (5/18) for MTBDRplus, 22% (4/18) for LCTB, and 61% (11/18) for Xpert MTB/RIF. A few (n = 5) RIF-resistant cases were detected using the phenotypic drug susceptibility testing methodology. Xpert MTB/RIF detected four of these five cases (fifth case not tested) and two additional phenotypically sensitive cases.
Conclusions
The Xpert MTB/RIF test has superior performance for rapid diagnosis of Mycobacterium tuberculosis over existing AFB smear microscopy and other molecular methodologies in an HIV- and TB-endemic region. Its place in the clinical diagnostic algorithm in national health programs needs exploration.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis (TB)—a contagious bacterial infection that mainly affects the lungs—is a global public health problem. In 2009, 9.4 million people developed TB, and 1.7 million people died from the disease; a quarter of these deaths were in HIV-positive individuals. People who are infected with HIV, the virus that causes AIDS, are particularly susceptible to TB because of their weakened immune system. Consequently, TB is a leading cause of illness and death among people living with HIV. TB is caused by Mycobacterium tuberculosis, which is spread in airborne droplets when people with the disease cough or sneeze. Its characteristic symptoms are a persistent cough, night sweats, and weight loss. Diagnostic tests for TB include sputum smear analysis (the microscopic examination of mucus brought up from the lungs by coughing for the presence of M. tuberculosis) and mycobacterial liquid culture (in which bacteriologists try to grow M. tuberculosis from sputum samples and test its drug sensitivity). TB can usually be cured by taking several powerful drugs daily for at least six months.
Why Was This Study Done?
Mycobacterial culture is a sensitive but slow way to diagnose TB. To halt the disease's spread, it is essential that TB—particularly TB that is resistant to several treatment drugs (multidrug-resistant, or MDR, TB)—is diagnosed quickly. Recently, several nucleic acid amplification technology (NAAT) tests have been developed that rapidly detect M. tuberculosis DNA in patient samples and look for DNA changes that make M. tuberculosis drug-resistant. In December 2010, the World Health Organization (WHO) endorsed Xpert MTB/RIF—an automated DNA test that detects M. tuberculosis and rifampicin resistance (an indicator of MDR TB) within two hours—for the investigation of patients who might have TB, especially in regions where MDR TB and HIV infection are common. TB diagnosis in HIV-positive people can be difficult because they are more likely to have smear-negative TB than HIV-negative individuals. In this prospective study, the researchers compare the performance of Xpert MTB/RIF on a single sputum sample with that of smear microscopy, liquid culture, and two other NAAT tests (MTBDRplus and LightCycler Mycobacterium Detection) in adults who might have TB in Johannesburg (South Africa), a region where many adults are HIV-positive.
What Did the Researchers Do and Find?
The researchers evaluated adults with potential TB attending a primary health care clinic for TB according to national guidelines and determined their HIV status. A sputum sample from 311 participants underwent smear microscopy, liquid culture, and drug susceptibility testing; 177 samples were also tested for TB using NAAT tests. They found that 70% of the participants were HIV-positive and 38.5% had culture-positive TB. Compared to liquid culture, smear microscopy, MTBDRplus, LightCycler Mycobacterium Detection, and Xpert MTB/RIF had sensitivities of 59%, 76%, 76%, and 86%, respectively. That is, assuming that liquid culture detected everyone with TB, Xpert MTB/RIF detected 86% of the cases. The specificity of all the tests compared to liquid culture was greater than 97%. That is, they all had a low false-positive rate. Among people who were HIV-positive, the sensitivity of Xpert MTB/RIF was 84%; the sensitivities of the other NAAT tests were 70%. Moreover, Xpert MTB/RIF detected TB in 61% of smear-negative, culture-positive samples, whereas the other NAATs detected TB in only about a quarter of these samples. Finally, although some TB cases were identified as drug-resistant by one test but drug-sensitive by another, the small number of drug-resistant cases means no firm conclusions can be made about the accuracy of drug resistance determination by the various tests.
What Do These Findings Mean?
Although these findings are likely to be affected by the study's small size, they suggest that Xpert MTB/RIF may provide a more accurate rapid diagnosis of TB than smear microscopy and other currently available NAAT tests in regions where HIV and TB are endemic (i.e., always present). Indeed, the reported accuracy of Xpert MTB/RIF for TB diagnosis—85% sensitivity and 97% specificity—has the potential to save more than 400,000 lives per year. Taken together with the results of other recent studies (including an accompanying article by Lawn et al. that investigates the use of Xpert MTB/RIF for screening for HIV-associated TB and rifampicin resistance), these findings support the WHO recommendation that Xpert MTB/RIF, rather than smear microscopy, should be the initial test in HIV-infected individuals who might have TB.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001061.
This study is further discussed in a PLoS Medicine Perspective by Carlton Evans; a related PLoS Medicine Research Article by Lawn et al. is also available
WHO provides information (in several languages) on all aspects of tuberculosis, including general information on tuberculosis diagnostics and specific information on the Xpert MTB/RIF test; further information about WHO's endorsement of Xpert MTB/RIF is included in a recent Strategic and Technical Advisory Group for Tuberculosis report
WHO also provides information about tuberculosis and HIV
The US National Institute of Allergy and Infectious Diseases has detailed information on tuberculosis and HIV/AIDS
The US Centers for Disease Control and Prevention also has information about tuberculosis, including information on the diagnosis of and on tuberculosis and HIV co-infection
Information is available from Avert, an international AIDS charity on many aspects of HIV/AIDS, including information on HIV-related tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001061
PMCID: PMC3144192  PMID: 21814495
8.  Direct microscopy versus sputum cytology analysis and bleach sedimentation for diagnosis of tuberculosis: a prospective diagnostic study 
BMC Infectious Diseases  2010;10:276.
Background
Diagnostic options for pulmonary tuberculosis in resource-poor settings are commonly limited to smear microscopy. We investigated whether bleach concentration by sedimentation and sputum cytology analysis (SCA) increased the positivity rate of smear microscopy for smear-positive tuberculosis.
Methods
We did a prospective diagnostic study in a Médecins Sans Frontières-supported hospital in Mindouli, Republic of Congo. Three sputum samples were obtained from 280 consecutive pulmonary tuberculosis suspects, and were processed according to WHO guidelines for direct smear microscopy. The remainder of each sputum sample was homogenised with 2.6% bleach, sedimented overnight, smeared, and examined blinded to the direct smear result for acid-fast bacilli (AFB). All direct smears were assessed for quality by SCA. If a patient produced fewer than three good-quality sputum samples, further samples were requested. Sediment smear examination was performed independently of SCA result on the corresponding direct smear. Positivity rates were compared using McNemar's test.
Results
Excluding SCA, 43.2% of all patients were diagnosed as positive on direct microscopy of up to three samples. 47.9% were diagnosed on sediment microscopy, with 48.2% being diagnosed on direct microscopy, sediment microscopy, or both. The positivity rate increased from 43.2% to 47.9% with a case definition of one positive smear (≥1 AFB/100 high power fields) of three, and from 42.1% to 43.9% with two positive smears. SCA resulted in 87.9% of patients producing at least two good-quality sputum samples, with 75.7% producing three or more. Using a case definition of one positive smear, the incremental yield of bleach sedimentation was 14/121, or 11.6% (95% CI 6.5-18.6, p = 0.001) and in combination with SCA was 15/121, or 12.4% (95% CI 7.1-19.6, p = 0.002). Incremental yields with two positive smears were 5/118, or 4.2% (95% CI 1.4-9.6, p = 0.062) and 7/118, or 5.9% (95% CI 2.4-11.8, p = 0.016), respectively.
Conclusions
The combination of bleach sedimentation and SCA resulted in significantly increased microscopy positivity rates with a case definition of either one or two positive smears. Implementation of bleach sedimentation led to a significant increase in the diagnosis of smear-positive patients. Implementation of SCA did not result in significantly increased diagnosis of tuberculosis, but did result in improved sample quality. Requesting extra sputum samples based on SCA results, combined with bleach sedimentation, could significantly increase the detection of smear-positive patients if routinely implemented in resource-limited settings where gold standard techniques are not available. We recommend that a pilot phase is undertaken before routine implementation to determine the impact in a particular context.
doi:10.1186/1471-2334-10-276
PMCID: PMC2946302  PMID: 20858253
9.  Commercial Serological Antibody Detection Tests for the Diagnosis of Pulmonary Tuberculosis: A Systematic Review 
PLoS Medicine  2007;4(6):e202.
Background
The global tuberculosis epidemic results in nearly 2 million deaths and 9 million new cases of the disease a year. The vast majority of tuberculosis patients live in developing countries, where the diagnosis of tuberculosis relies on the identification of acid-fast bacilli on unprocessed sputum smears using conventional light microscopy. Microscopy has high specificity in tuberculosis-endemic countries, but modest sensitivity which varies among laboratories (range 20% to 80%). Moreover, the sensitivity is poor for paucibacillary disease (e.g., pediatric and HIV-associated tuberculosis). Thus, the development of rapid and accurate new diagnostic tools is imperative. Immune-based tests are potentially suitable for use in low-income countries as some test formats can be performed at the point of care without laboratory equipment. Currently, dozens of distinct commercial antibody detection tests are sold in developing countries. The question is “do they work?”
Methods and Findings
We conducted a systematic review to assess the accuracy of commercial antibody detection tests for the diagnosis of pulmonary tuberculosis. Studies from all countries using culture and/or microscopy smear for confirmation of pulmonary tuberculosis were eligible. Studies with fewer than 50 participants (25 patients and 25 control participants) were excluded. In a comprehensive search, we identified 68 studies. The results demonstrate that (1) overall, commercial tests vary widely in performance; (2) sensitivity is higher in smear-positive than smear-negative samples; (3) in studies of smear-positive patients, Anda-TB IgG by enzyme-linked immunosorbent assay shows limited sensitivity (range 63% to 85%) and inconsistent specificity (range 73% to 100%); (4) specificity is higher in healthy volunteers than in patients in whom tuberculosis disease is initially suspected and subsequently ruled out; and (5) there are insufficient data to determine the accuracy of most commercial tests in smear microscopy–negative patients, as well as their performance in children or persons with HIV infection.
Conclusions
None of the commercial tests evaluated perform well enough to replace sputum smear microscopy. Thus, these tests have little or no role in the diagnosis of pulmonary tuberculosis. Lack of methodological rigor in these studies was identified as a concern. It will be important to review the basic science literature evaluating serological tests for the diagnosis of pulmonary tuberculosis to determine whether useful antigens have been described but their potential has not been fully exploited. Activities leading to the discovery of new antigens with immunodiagnostic potential need to be intensified.
Based on a systematic review, Madhukar Pai and colleagues conclude that none of the commercial immune-based tests for pulmonary tuberculosis so far evaluated perform well enough to replace sputum smear microscopy.
Editors' Summary
Background.
Tuberculosis (TB) is, globally, one of the most important infectious diseases. It is thought that in 2005 around 1.6 million people died as a result of TB. Controlling TB requires that the disease is correctly diagnosed so that it can then be promptly treated, which will reduce the risk of infection being passed on to other individuals. The method normally used for diagnosing TB disease in poor countries (where most people with TB disease live) involves taking a sample of mucus coughed up from the lungs; this mucus is then spread thinly onto a glass slide, dyed, and viewed under the microscope. The bacteria responsible for TB take up the dye in a particular pattern and can be clearly seen under the microscope. Although this test (sputum smear) is relatively straightforward to carry out even where facilities are basic, it is not particularly good at identifying TB disease in children or amongst individuals who are HIV-positive. Finally, the sputum smear test is also not very sensitive; that is, many people who have TB disease may not give a positive reading. Therefore, there is an urgent need to develop and evaluate new tests that are suitable for use in poor countries, which will accurately diagnose TB disease, especially amongst children and people who are HIV-positive.
Why Was This Study Done?
New tests for TB have become available which detect whether an individual has raised antibodies against particular proteins and other substances present on the surface of the TB bacterium. These tests are carried out on blood samples, once blood cells and other factors have been taken out. These antibody tests are often quite simple to carry out, so in principle they could be suitable for use in developing countries. Since the tests are available on the market and can be freely used in some developing countries without any need for government regulatory bodies to approve them, it is important to know how good these tests are at diagnosing TB disease. The researchers here wanted, therefore, to evaluate all of the available data relating to the accuracy of antibody detection tests for diagnosis of TB disease.
What Did the Researchers Do and Find?
In order to evaluate all of the information available on commercial antibody detection tests for diagnosis of TB disease of the lungs, the researchers carried out a systematic review. First, they searched biomedical literature databases using specific terms to identify studies for inclusion. A study was included in their analysis if the commercial test was compared against one of two other standard tests (sputum smear microscopy, or growth of TB bacteria in culture). One researcher from the team then pulled out specific pieces of information from each published study: these included the type of study design; information on study participants; the type of test; what the test was compared against; and finally the results of evaluation of the test. A second researcher pulled out pieces of information from several of the same studies. The researchers then compared the information to ensure that it was recorded correctly. Each study was also assigned a quality rating, based on four distinct criteria. For each type of test, the researchers used the data in the published studies to work out the test's accuracy, both in terms of its ability to give a positive reading for people who have TB disease as well as its ability to give a negative reading for people who do not have TB disease.
The researchers found 27 papers meeting their criteria. These papers reported the results of 68 original studies. Nine different commercial tests were examined in the studies. Overall, the studies seemed to be of relatively poor quality, with only 25% of them meeting all four of the researchers' criteria for a good-quality study. The different studies appeared to produce varying results for the accuracy of these commercial tests. In particular, the tests seemed to be less accurate at detecting TB disease amongst people who had a negative sputum smear than amongst people with a positive sputum smear. When all the data for these different studies were combined, the statistics indicated that the commercial tests, overall, were only modestly accurate for diagnosis of TB disease. None of the studies had been carried out in children or in HIV-positive people.
What Do These Findings Mean?
The results of this systematic review suggest that the commercial antibody detection tests considered here are not particularly useful in diagnosis of TB disease as compared to other tests, such as sputum smear and bacterial culture. Some people are concerned that there is pressure in certain developing countries to start using these tests, but the current data do not support greater use. This systematic review also highlights the fact that many studies evaluating commercial TB tests are of poor quality, and that further research needs to be done to evaluate the accuracy of different TB tests amongst children and HIV-positive patients.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040202.
World Health Organization Stop TB Department website. Information about the current Stop TB strategy, data and factsheets about TB, and other resources are available
Questions and Answers about Tuberculosis provided by the US Centers for Disease Control and Prevention
Information about TB tests from Médicins sans Frontières (MSF). Links to MSF reports on new diagnostic tests are also available
Wikipedia entry on Systematic Reviews (Note: Wikipedia is an internet encyclopedia anyone can edit)
doi:10.1371/journal.pmed.0040202
PMCID: PMC1891320  PMID: 17564490
10.  Accuracy of the Xpert MTB/RIF test for the diagnosis of pulmonary tuberculosis in children admitted to hospital in Cape Town, South Africa: a descriptive study 
The Lancet. Infectious diseases  2011;11(11):819-824.
Summary
Background
WHO recommends that Xpert MTB/RIF replaces smear microscopy for initial diagnosis of suspected HIV-associated tuberculosis or multidrug-resistant pulmonary tuberculosis, but no data exist for its use in children. We aimed to assess the accuracy of the test for the diagnosis of pulmonary tuberculosis in children in an area with high tuberculosis and HIV prevalences.
Methods
In this prospective, descriptive study, we enrolled children aged 15 years or younger who had been admitted to one of two hospitals in Cape Town, South Africa, with suspected pulmonary tuberculosis between Feb 19, 2009, and Nov 30, 2010. We compared the diagnostic accuracy of MTB/RIF and concentrated, fluorescent acid-fast smear with a reference standard of liquid culture from two sequential induced sputum specimens (primary analysis).
Results
452 children (median age 19·4 months, IQR 11·1–46·2) had at least one induced sputum specimen; 108 children (24%) had HIV infection. 27 children (6%) had a positive smear result, 70 (16%) had a positive culture result, and 58 (13%) had a positive MTB/RIF test result. With mycobacterial culture as the reference standard, MTB/RIF tests when done on two induced sputum samples detected twice as many cases (75·9%, 95% CI 64·5–87·2) as did smear microscopy (37·9%, 25·1–50·8), detecting all of 22 smear-positive cases and 22 of 36 (61·1%, 44·4–77·8) smear-negative cases. For smear-negative cases, the incremental increase in sensitivity from testing a second specimen was 27·8% for MTB/RIF, compared with 13·8% for culture. The specificity of MTB/RIF was 98·8% (97·6–99·9). MTB/RIF results were available in median 1 day (IQR 0–4) compared with median 12 days (9–17) for culture (p<0·0001).
Interpretation
MTB/RIF testing of two induced sputum specimens is warranted as the first-line diagnostic test for children with suspected pulmonary tuberculosis.
Funding
National Institutes of Health, the National Health Laboratory Service Research Trust, the Medical Research Council of South Africa, and Wellcome Trust.
doi:10.1016/S1473-3099(11)70167-0
PMCID: PMC4202386  PMID: 21764384
11.  Impact of Replacing Smear Microscopy with Xpert MTB/RIF for Diagnosing Tuberculosis in Brazil: A Stepped-Wedge Cluster-Randomized Trial 
PLoS Medicine  2014;11(12):e1001766.
Betina Durovni and colleagues evaluated whether implementation of Xpert MTB/RIF increased the notification rate of laboratory-confirmed pulmonary tuberculosis and reduced the time to tuberculosis treatment initiation in 14 Brazilian primary care laboratories.
Please see later in the article for the Editors' Summary
Background
Abundant evidence on Xpert MTB/RIF accuracy for diagnosing tuberculosis (TB) and rifampicin resistance has been produced, yet there are few data on the population benefit of its programmatic use. We assessed whether the implementation of Xpert MTB/RIF in routine conditions would (1) increase the notification rate of laboratory-confirmed pulmonary TB to the national notification system and (2) reduce the time to TB treatment initiation (primary endpoints).
Methods and Findings
We conducted a stepped-wedge cluster-randomized trial from 4 February to 4 October 2012 in 14 primary care laboratories in two Brazilian cities. Diagnostic specimens were included for 11,705 baseline (smear microscopy) and 12,522 intervention (Xpert MTB/RIF) patients presumed to have TB. Single-sputum-sample Xpert MTB/RIF replaced two-sputum-sample smear microscopy for routine diagnosis of pulmonary TB. In total, 1,137 (9.7%) tests in the baseline arm and 1,777 (14.2%) in the intervention arm were positive (p<0.001), resulting in an increased bacteriologically confirmed notification rate of 59% (95% CI = 31%, 88%). However, the overall notification rate did not increase (15%, 95% CI = −6%, 37%), and we observed no change in the notification rate for those without a test result (−3%, 95% CI = −37%, 30%). Median time to treatment decreased from 11.4 d (interquartile range [IQR] = 8.5–14.5) to 8.1 d (IQR = 5.4–9.3) (p = 0.04), although not among confirmed cases (median 7.5 [IQR = 4.9–10.0] versus 7.3 [IQR = 3.4–9.0], p = 0.51). Prevalence of rifampicin resistance detected by Xpert was 3.3% (95% CI = 2.4%, 4.3%) among new patients and 7.4% (95% CI = 4.3%, 11.7%) among retreatment patients, with a 98% (95% CI = 87%, 99%) positive predictive value compared to phenotypic drug susceptibility testing. Missing data in the information systems may have biased our primary endpoints. However, sensitivity analyses assessing the effects of missing data did not affect our results.
Conclusions
Replacing smear microscopy with Xpert MTB/RIF in Brazil increased confirmation of pulmonary TB. An additional benefit was the accurate detection of rifampicin resistance. However, no increase on overall notification rates was observed, possibly because of high rates of empirical TB treatment.
Trial registration
ClinicalTrials.gov NCT01363765
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis—a contagious bacterial disease that usually infects the lungs—is a global public health problem. Each year, about 8.6 million people develop active tuberculosis and at least 1.3 million people die from the disease, mainly in resource-limited countries. Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is spread in airborne droplets when people with active disease cough or sneeze. The characteristic symptoms of tuberculosis include cough, weight loss, and night sweats. Diagnostic tests for tuberculosis include sputum smear microscopy (microscopic analysis of mucus coughed up from the lungs), the growth (culture) of M. tuberculosis from sputum samples, and molecular tests (for example, the Xpert MTB/RIF test) that rapidly and accurately detect M. tuberculosis in sputum and determine its antibiotic resistance. Tuberculosis can be cured by taking several antibiotics daily for at least six months, although the emergence of multidrug-resistant tuberculosis is making the disease increasingly hard to treat.
Why Was This Study Done?
Quick, accurate diagnosis of active tuberculosis is essential to reduce the global tuberculosis burden, but in most high-burden settings diagnosis relies on sputum smear analysis, which fails to identify many infected people. Mycobacterial culture correctly identifies more infected people but is slow, costly, and rarely available in resource-limited settings. In late 2010, therefore, the World Health Organization recommended the routine use of the Xpert MTB/RIF assay (Xpert) for tuberculosis diagnosis, and several resource-limited countries are currently scaling up the use of Xpert in their national tuberculosis control programs. However, although Xpert works well in ideal conditions, little is known about its performance in routine (real-life) settings. In this pragmatic stepped-wedge cluster-randomized trial, the researchers assess the impact of replacing smear microscopy with Xpert for the diagnosis of tuberculosis in Brazil, an upper-middle-income country with a high tuberculosis burden. A pragmatic trial asks whether an intervention works under real-life conditions; a stepped-wedge cluster-randomized trial sequentially and randomly rolls out an intervention to groups (clusters) of people.
What Did the Researchers Do and Find?
The researchers randomly assigned 14 tuberculosis diagnosis laboratories in two cities to switch at different times from smear microscopy to Xpert for tuberculosis diagnosis. Specifically, at the start of the eight-month trial, all the laboratories used smear microscopy for tuberculosis diagnosis. At the end of each month, two laboratories switched to using Xpert, so that in the final month of the trial, all the laboratories were using Xpert. During the trial, 11,705 samples from patients with symptoms consistent with tuberculosis were examined using smear microscopy (baseline arm), and 12,522 samples were examined using Xpert (intervention arm). The researchers obtained the results of these tests from a database of all the diagnostic tests ordered in the Brazilian public laboratory system, and they obtained data on tuberculosis notifications during the trial period from the national notification system. In total, 9.7% and 14.2% of the tests in the baseline and intervention arm, respectively, were positive, and the laboratory-confirmed tuberculosis notification rate was 1.59 times higher in the Xpert arm than in the smear microscopy arm. However, the overall notification rate (which included people who began treatment on the basis of symptoms alone) did not increase during the trial. The time to treatment (the time between the laboratory test date and the notification date, when treatment usually starts in Brazil) was about 11 days and eight days in the smear microscopy and Xpert arms, respectively.
What Do These Findings Mean?
The findings indicate that, in a setting where laboratory diagnosis for tuberculosis was largely restricted to sputum smear examination, the implementation of Xpert increased the rates of laboratory-confirmed pulmonary (lung) tuberculosis notifications and reduced the time to treatment initiation, two endpoints of public health relevance. However, implementation of Xpert did not increase the overall notification rate of pulmonary tuberculosis (probably because of the high rate of empiric tuberculosis treatment in Brazil), although it did facilitate accurate and rapid detection of rifampicin resistance. The accuracy of these findings may be limited by certain aspects of the trial design, and further studies are needed to evaluate the possible effects of Xpert beyond diagnosis and the time to treatment initiation. Nevertheless, these findings suggest that replacing smear microscopy with Xpert has the potential to increase the confirmation (but not detection) of pulmonary tuberculosis and to reduce the time to treatment initiation at the population level in Brazil and other resource-limited countries.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001766.
The World Health Organization (WHO) provides information (in several languages) on tuberculosis, on tuberculosis diagnostics, and on the rollout of Xpert; further information about WHO's endorsement of Xpert is included in a Strategic and Technical Advisory Group for Tuberculosis report; the “Global Tuberculosis Report 2013” provides information about tuberculosis around the world, including Brazil
The Stop TB Partnership is working towards tuberculosis elimination and provides patient stories about tuberculosis (in English and Spanish); the Tuberculosis Vaccine Initiative (a not-for-profit organization) also provides personal stories about tuberculosis
The US Centers for Disease Control and Prevention provides information about tuberculosis and its diagnosis (in English and Spanish)
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
More information about this trial is available
doi:10.1371/journal.pmed.1001766
PMCID: PMC4260794  PMID: 25490549
12.  Cost-effectiveness analysis of PCR for the rapid diagnosis of pulmonary tuberculosis 
Background
Tuberculosis is one of the most prominent health problems in the world, causing 1.75 million deaths each year. Rapid clinical diagnosis is important in patients who have co-morbidities such as Human Immunodeficiency Virus (HIV) infection. Direct microscopy has low sensitivity and culture takes 3 to 6 weeks [1-3]. Therefore, new tools for TB diagnosis are necessary, especially in health settings with a high prevalence of HIV/TB co-infection.
Methods
In a public reference TB/HIV hospital in Brazil, we compared the cost-effectiveness of diagnostic strategies for diagnosis of pulmonary TB: Acid fast bacilli smear microscopy by Ziehl-Neelsen staining (AFB smear) plus culture and AFB smear plus colorimetric test (PCR dot-blot).
From May 2003 to May 2004, sputum was collected consecutively from PTB suspects attending the Parthenon Reference Hospital. Sputum samples were examined by AFB smear, culture, and PCR dot-blot. The gold standard was a positive culture combined with the definition of clinical PTB. Cost analysis included health services and patient costs.
Results
The AFB smear plus PCR dot-blot require the lowest laboratory investment for equipment (US$ 20,000). The total screening costs are 3.8 times for AFB smear plus culture versus for AFB smear plus PCR dot blot costs (US$ 5,635,760 versus US$ 1,498, 660). Costs per correctly diagnosed case were US$ 50,773 and US$ 13,749 for AFB smear plus culture and AFB smear plus PCR dot-blot, respectively. AFB smear plus PCR dot-blot was more cost-effective than AFB smear plus culture, when the cost of treating all correctly diagnosed cases was considered. The cost of returning patients, which are not treated due to a negative result, to the health service, was higher in AFB smear plus culture than for AFB smear plus PCR dot-blot, US$ 374,778,045 and US$ 110,849,055, respectively.
Conclusion
AFB smear associated with PCR dot-blot associated has the potential to be a cost-effective tool in the fight against PTB for patients attended in the TB/HIV reference hospital.
doi:10.1186/1471-2334-9-216
PMCID: PMC2811112  PMID: 20043842
13.  Diagnostic Accuracy of Quantitative PCR (Xpert MTB/RIF) for Tuberculous Meningitis in a High Burden Setting: A Prospective Study 
PLoS Medicine  2013;10(10):e1001536.
Vinod Patel and colleagues evaluate the sensitivity and specificity of quantitative PCR using Xpert MTB/RIF for diagnosis of TB meningitis in the high-burden setting of South Africa.
Please see later in the article for the Editors' Summary
Background
Tuberculous meningitis (TBM) is difficult to diagnose promptly. The utility of the Xpert MTB/RIF test for the diagnosis of TBM remains unclear, and the effect of host- and sample-related factors on test performance is unknown. This study sought to evaluate the sensitivity and specificity of Xpert MTB/RIF for the diagnosis of TBM.
Methods and Findings
235 South-African patients with a meningeal-like illness were categorised as having definite (culture or Amplicor PCR positive), probable (anti-TBM treatment initiated but microbiological confirmation lacking), or non-TBM. Xpert MTB/RIF accuracy was evaluated using 1 ml of uncentrifuged and, when available, 3 ml of centrifuged cerebrospinal fluid (CSF). To evaluate the incremental value of MTB/RIF over a clinically based diagnosis, test accuracy was compared to a clinical score (CS) derived using basic clinical and laboratory information.
Of 204 evaluable patients (of whom 87% were HIV-infected), 59 had definite TBM, 64 probable TBM, and 81 non-TBM. Overall sensitivity and specificity (95% CI) were 62% (48%–75%) and 95% (87%–99%), respectively. The sensitivity of Xpert MTB/RIF was significantly better than that of smear microscopy (62% versus 12%; p = 0.001) and significantly better than that of the CS (62% versus 30%; p = 0.001; C statistic 85% [79%–92%]). Xpert MTB/RIF sensitivity was higher when centrifuged versus uncentrifuged samples were used (82% [62%–94%] versus 47% [31%–61%]; p = 0.004). The combination of CS and Xpert MTB/RIF (Xpert MTB/RIF performed if CS<8) performed as well as Xpert MTB/RIF alone but with a ∼10% reduction in test usage. This overall pattern of results remained unchanged when the definite and probable TBM groups were combined. Xpert MTB/RIF was not useful in identifying TBM among HIV-uninfected individuals, although the sample was small. There was no evidence of PCR inhibition, and the limit of detection was ∼80 colony forming units per millilitre. Study limitations included a predominantly HIV-infected cohort and the limited number of culture-positive CSF samples.
Conclusions
Xpert MTB/RIF may be a good rule-in test for the diagnosis of TBM in HIV-infected individuals from a tuberculosis-endemic setting, particularly when a centrifuged CSF pellet is used. Further studies are required to confirm these findings in different settings.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Worldwide, tuberculosis (TB) is the leading cause of death among people living with HIV. The risk of developing TB is estimated to be 12–20 times greater in people with HIV than in people without HIV. The World Health Organization reported that, in 2011, there were 8.7 million new cases of TB, of which 1.1 million were among people living with HIV. TB infection in people living with HIV is a major problem in sub-Saharan Africa, where up to 80% of individuals infected with TB are also infected with HIV.
TB is caused by a bacterial infection spread through the air from one person to another when the infected person coughs or sneezes, for example. It usually affects the lungs, but it can also affect other parts of the body including the brain, where it leads to meningitis. People with meningitis caused by TB are often seriously ill. Many may develop brain damage, and 30% will die, particularly if they aren't diagnosed quickly and treatment is delayed. TB meningitis is therefore a serious health concern in countries with high rates of HIV and TB co-infection.
Why Was This Study Done?
There is currently no simple test to diagnose TB meningitis. The tests that are available detect only about 50% of cases. They are expensive and practical to use only in a high-tech environment, and are therefore unsuitable for low-income countries.
Recently, a new test has become available to detect TB, known as Xpert MTB/RIF. The test is used to detect the DNA (the molecular biological instructions for each organism) of the bacteria that causes TB. It is accurate at detecting TB lung infection, requires minimal training to operate, and is relatively inexpensive. It is now being used to diagnose TB in countries with high rates of the disease, including South Africa. However, thus far its use has been limited to detecting the TB bacterium in sputum samples (a mixture of saliva and phlegm) from people with a lung infection. The few studies that have assessed whether the test can be used to detect TB meningitis have been small and inconclusive.
This study was carried out to determine whether Xpert MTB/RIF could be used to detect TB bacteria in the cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) in people with TB meningitis. The researchers wanted to find out whether the test would be sensitive (correctly identifying patients with TB meningitis) and specific (correctly identifying patients without TB meningitis). They also wanted to address more practical questions such as how much cerebrospinal fluid needs to be collected and how the sample needs to be processed to ensure accurate results.
What Did the Researchers Do and Find?
The researchers used the Xpert MTB/RIF test to analyze cerebrospinal fluid samples from 204 patients with suspected TB meningitis. These patients were recruited from hospitals in South Africa between January 2008 and December 2011.
Standard diagnostic tests were used to categorize these patients as either definitely having TB meningitis, possibly having TB meningitis, or not having TB meningitis. Among patients infected with HIV, the Xpert MTB/RIF correctly identified 62% of those with TB meningitis and 95% of those without TB meningitis.
The researchers also assessed whether it would be more cost-effective to use the test only for cases where the standard diagnostic procedure was uncertain, i.e., to avoid testing in cases where TB meningitis was very likely following the normal clinical assessment. Based on the researchers' theoretical analysis, this would reduce test use by only about 10%.
What Do These Findings Mean?
This study suggests that Xpert MTB/RIF is a useful diagnostic test for TB meningitis in patients infected with HIV living in areas where there are high levels of TB infection. It is not known how well the test would perform in places where TB levels are low, and the test did not perform well in individuals without HIV, although there were very few of these patients. The Xpert MTB/RIF test correctly identified more positive cases than the other tests used to diagnose TB meningitis, within 24 hours of first seeing a patient. However, the test accuracy was best when the cerebrospinal fluid sample was centrifuged (spinning the sample very fast to concentrate the test material) to achieve the best results. This means additional apparatus would be required, resulting in higher cost and requiring more training. The researchers conclude that this test could still be useful in settings where resources are limited.
There are also important questions that remain unanswered. This study shows only that the Xpert MTB/RIF test is useful in determining that a patient has TB meningitis. It is not useful in determining that a patient does not have TB meningitis. Further research is needed to determine whether the test will be effective in areas with lower rates of TB, as well as whether its use will improve clinical practice and ultimately lead to better outcomes for patients. The hope is that the test will result in more rapid diagnosis and faster treatment, reducing the number of avoidable deaths from TB meningitis.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001536.
• This study is further discussed in a PLOS Medicine Perspective by David Boulware
• The US National Institutes of Health provides information on TB meningitis
• The World Health Organization provides information on tuberculosis and HIV
• The US Centers for Disease Control and Prevention has a factsheet on HIV and TB
• AIDS.gov also provides information about HIV and TB
doi:10.1371/journal.pmed.1001536
PMCID: PMC3805498  PMID: 24167451
14.  Diagnostic accuracy of a low-cost, urine antigen, point-of-care screening assay for HIV-associated pulmonary tuberculosis before antiretroviral therapy: a descriptive study 
The Lancet Infectious Diseases  2012;12(3):201-209.
Summary
Background
The diagnostic accuracy of sputum smear microscopy and routine chest radiology for HIV-associated tuberculosis is poor, and culture-based diagnosis is slow, expensive, and is unavailable in most resource-limited settings. We assessed the diagnostic accuracy of a urine antigen test Determine TB-LAM Ag (Determine TB-LAM; Alere, Waltham, MA, USA) for screening for HIV-associated pulmonary tuberculosis before antiretroviral therapy (ART).
Methods
In this descriptive study, consecutive adults referred to a community-based ART clinic in Gugulethu township, South Africa, were all screened for tuberculosis by obtaining sputum samples for fluorescence microscopy, automated liquid culture (gold-standard test), and Xpert MTB/RIF assays (Cepheid, Sunnyvale, CA, USA) and urine samples for the Clearview TB-ELISA (TB-ELISA; Alere, Waltham, MA, USA) and Determine TB-LAM test. Patients with Mycobacterium tuberculosis cultured from one or more sputum samples were defined as cases of tuberculosis. The diagnostic accuracy of Determine TB-LAM used alone or combined with sputum smear microscopy was compared with that of sputum culture and the Xpert MTB/RIF assay for all patients and subgroups of patients stratified by CD4 cell count.
Findings
Patients were recruited between March 12, 2010, and April 20, 2011. Of 602 patients enrolled, 542 were able to provide one or more sputum samples, and 94 had culture-positive tuberculosis (prevalence 17·4%, 95% CI 14·2–20·8). Complete results from all tests were available for 516 patients (median CD4 count, 169·5 cells per μL; IQR 100–233), including 85 culture-positive tuberculosis, 24 of whom (28·2%, 95% CI 19·0–39·0) had sputum smear-positive disease. Determine TB-LAM test strips provided results within 30 min. Agreement was very high between two independent readers of the test strips (κ=0·97) and between the test strips and TB-ELISA (κ=0·84). Determine TB-LAM had highest sensitivity at low CD4 cell counts: 66·7% (95% CI 41·0–86·7) at <50 cells per μL, 51·7% (32·5–70·6) at <100 cells per μL, and 39·0% (26·5–52·6) at <200 cells per μL; specificity was greater than 98% for all strata. When combined with smear microscopy (either test positive), sensitivity was 72·2% (95% CI 46·5–90·3) at CD4 counts less than 50 cells per μL, 65·5% (45·7–82·1) at less than 100 cells per μL, and 52·5% (39·1–65·7) at less than 200 cells per μL, which did not differ statistically from the sensitivities obtained by testing a single sputum sample with the Xpert MTB/RIF assay.
Interpretation
Determine TB-LAM is a simple, low-cost, alternative to existing diagnostic assays for tuberculosis screening in HIV-infected patients with very low CD4 cell counts and provides important incremental yield when combined with sputum smear microscopy.
Funding
Wellcome Trust.
doi:10.1016/S1473-3099(11)70251-1
PMCID: PMC3315025  PMID: 22015305
15.  Comparison of the Efficacies of Loop-Mediated Isothermal Amplification, Fluorescence Smear Microscopy and Culture for the Diagnosis of Tuberculosis 
PLoS ONE  2011;6(6):e21007.
Background
Despite the advent of novel diagnostic techniques, smear microscopy remains as the most practical test available in resource-limited settings for tuberculosis (TB) diagnosis. Due to the low sensitivity of microscopy and the long time required for culture, feasible and accessible rapid diagnostic methods are urgently needed. Loop-mediated Isothermal Amplification (LAMP) is a promising nucleic-acid amplification assay, which could be accessible, cost-effective and more suited for use with unpurified samples.
Methodology/Principal Findings
In the current study, the objective was to assess the efficacy of a LAMP assay for tuberculosis compared with fluorescence smear microscopy as well as Löwenstein-Jensen (LJ) and Mycobacteria Growth Indicator Tube (MGIT) cultures for the diagnosis of pulmonary tuberculosis using sputum samples. Smear microscopy and culture were performed for decontaminated and concentrated sputum from TB suspects and the LAMP was also performed on these specimens. The LAMP and smear microscopy were compared, in series and in parallel, to culture. LAMP and smear microscopy showed sensitivities of 79.5% and 82.1% respectively and specificities of 93.8% and 96.9% respectively, compared to culture. LAMP and smear in series had sensitivity and specificity of 79.5% and 100.0% respectively. LAMP and smear in parallel had sensitivity and specificity of 82.1% and 90.6% respectively.
Conclusions/Significance
The overall efficacies of LAMP and fluorescence smear microscopy in the current study were high and broadly similar. LAMP and smear in series had high specificity (100.0%) and can be used as a rule-in test combination. However, the performance of LAMP in smear negative samples was found to be insufficient.
doi:10.1371/journal.pone.0021007
PMCID: PMC3117872  PMID: 21695047
16.  Rapid Molecular Diagnosis of Pulmonary Tuberculosis in Children Using Nasopharyngeal Specimens 
Xpert testing enables the rapid diagnosis of childhood tuberculosis using 2 nasopharyngeal aspirates (NPA) or 2 induced sputum (IS) specimens with a sensitivity of 65% and 71%, respectively, and high specificity. Two IS specimens provide a higher yield than 2 NPAs for culture confirmation.
Background. A rapid diagnosis of pediatric pulmonary tuberculosis (PTB) using Xpert MTB/RIF (Mycobacterium tuberculosis/rifampicin) automated testing on induced sputum (IS) is possible, but the capacity for performing IS is limited. The diagnosis using a nasopharyngeal aspirate (NPA), which can be non-invasively obtained, is desirable.
Methods. Paired specimens (NPA and IS) were tested using smear, liquid culture and Xpert. The diagnostic accuracy of Xpert and smear was compared with culture for different specimens in children with suspected PTB.
Results. There were 535 children [median age 19 months, 117 (21·9%) HIV-infected] who had one IS and one NPA specimen; 396 had two paired specimens. A positive smear, Xpert test or culture occurred in 30 (5.6%), 81 (15.1%) and 87 children (16.3%), respectively. The culture yield was higher from IS (84/87, 96.6%) vs NPA (61/87, 70.1%, P < .001). Amongst children with two paired specimens, 63 culture-confirmed cases occurred [60 (95.2%) IS vs 48 (76.2%) NPA, P = .002]. The sensitivity of two Xpert tests was similar for IS and NPAs [(45/63) 71% vs (41/63) 65%, P = .444)]; the sensitivity of smear was lower for IS (21/63, 33%) and NPA (16/63, 25%). The incremental yield from a second IS was 9 cases (17.6%) by culture and 9 (25%) by Xpert testing; a second NPA increased the culture yield by 10 (26.3%) and Xpert by 11 (36.7%). Xpert specificity was 99.1% (98.1–100) for IS and 98.2% (96.8–99.6) for NPAs. Xpert testing provided faster results than culture (median 0 vs 15 days, P < .001).
Conclusions. Xpert testing on 2 NPAs is useful in children with suspected PTB, particularly in settings where IS and culture are not feasible.
doi:10.1093/cid/cis598
PMCID: PMC3529610  PMID: 22752518
17.  Detection of Tuberculosis in HIV-Infected and -Uninfected African Adults Using Whole Blood RNA Expression Signatures: A Case-Control Study 
PLoS Medicine  2013;10(10):e1001538.
Using a microarray-based approach, Michael Levin and colleagues develop a disease risk score to distinguish active from latent tuberculosis, as well as tuberculosis from other diseases, using whole blood samples.
Please see later in the article for the Editors' Summary
Background
A major impediment to tuberculosis control in Africa is the difficulty in diagnosing active tuberculosis (TB), particularly in the context of HIV infection. We hypothesized that a unique host blood RNA transcriptional signature would distinguish TB from other diseases (OD) in HIV-infected and -uninfected patients, and that this could be the basis of a simple diagnostic test.
Methods and Findings
Adult case-control cohorts were established in South Africa and Malawi of HIV-infected or -uninfected individuals consisting of 584 patients with either TB (confirmed by culture of Mycobacterium tuberculosis [M.TB] from sputum or tissue sample in a patient under investigation for TB), OD (i.e., TB was considered in the differential diagnosis but then excluded), or healthy individuals with latent TB infection (LTBI). Individuals were randomized into training (80%) and test (20%) cohorts. Blood transcriptional profiles were assessed and minimal sets of significantly differentially expressed transcripts distinguishing TB from LTBI and OD were identified in the training cohort. A 27 transcript signature distinguished TB from LTBI and a 44 transcript signature distinguished TB from OD. To evaluate our signatures, we used a novel computational method to calculate a disease risk score (DRS) for each patient. The classification based on this score was first evaluated in the test cohort, and then validated in an independent publically available dataset (GSE19491).
In our test cohort, the DRS classified TB from LTBI (sensitivity 95%, 95% CI [87–100]; specificity 90%, 95% CI [80–97]) and TB from OD (sensitivity 93%, 95% CI [83–100]; specificity 88%, 95% CI [74–97]). In the independent validation cohort, TB patients were distinguished both from LTBI individuals (sensitivity 95%, 95% CI [85–100]; specificity 94%, 95% CI [84–100]) and OD patients (sensitivity 100%, 95% CI [100–100]; specificity 96%, 95% CI [93–100]).
Limitations of our study include the use of only culture confirmed TB patients, and the potential that TB may have been misdiagnosed in a small proportion of OD patients despite the extensive clinical investigation used to assign each patient to their diagnostic group.
Conclusions
In our study, blood transcriptional signatures distinguished TB from other conditions prevalent in HIV-infected and -uninfected African adults. Our DRS, based on these signatures, could be developed as a test for TB suitable for use in HIV endemic countries. Further evaluation of the performance of the signatures and DRS in prospective populations of patients with symptoms consistent with TB will be needed to define their clinical value under operational conditions.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis (TB), caused by Mycobacterium tuberculosis, is curable and preventable, but according to the World Health Organization (WHO), in 2011, 8.7 million people had symptoms of TB (usually a productive cough and fever) and 1.4 million people—95% from low- and middle-income countries—died from this infection. Worldwide, TB is also the leading cause of death in people with HIV. For over a century, diagnosis of TB has relied on clinical and radiological features, sputum microscopy, and tuberculin skin testing but all of these tests have major disadvantages, especially in people who are also infected with HIV (HIV/TB co-infection) in whom results are often atypical or falsely negative. Furthermore, current tests cannot distinguish between inactive (latent) and active TB infection. Therefore, there is a need to identify biomarkers that can differentiate TB from other diseases common to African populations, where the burden of the HIV/TB pandemic is greatest.
Why Was This Study Done?
Previous studies have suggested that TB may be associated with specific transcriptional profiles (identified by microarray analysis) in the blood of the infected patient (host), which might make it possible to differentiate TB from other conditions. However, these studies have not included people co-infected with HIV and have included in the differential diagnosis diseases that are unrepresentative of the range of conditions common to African patients. In this study of patients from Malawi and South Africa, the researchers investigated whether blood RNA expression could distinguish TB from other conditions prevalent in African populations and form the basis of a diagnostic test for TB (through a process using transcription signatures).
What Did the Researchers Do and Find?
The researchers recruited patients with suspected TB attending one clinic in Cape Town, South Africa between 2007 and 2010 and in one hospital in Karonga district, Malawi between 2007 and 2009 (the training and test cohorts). Each patient underwent a series of tests for TB (and had a blood test for HIV) and was diagnosed as having TB if there was microbiological evidence confirming the presence of Mycobacterium tuberculosis. At recruitment, each patient also had blood taken for microarray analysis and following this assessment, the researchers selected minimal transcript sets that distinguished TB from latent TB infection and TB from other diseases, even in HIV-infected individuals. In order to help form the basis of a simple, low cost, diagnostic test, the researchers then developed a statistical method for the translation of multiple transcript RNA signatures into a disease risk score, which the researchers then checked using a separate cohort of South African patients (the independent validation cohort).
Using these methods, after screening 437 patients in Malawi and 314 in South Africa, the researchers recruited 273 patients to the Malawi cohort and 311 adults to the South African cohort (the training and test cohorts). Following technical failures, 536 microarray samples were available for analysis. The researchers identified a set of 27 transcripts that could distinguish between TB and latent TB and a set of 44 transcripts that could distinguish TB from other diseases. These multi-transcript signatures were then used to calculate a single value disease risk score for every patient. In the test cohorts, the disease risk score had a high sensitivity (95%) and specificity (90%) for distinguishing TB from latent TB infection (sensitivity is a measure of true positives, correctly identified as such and specificity is a measure of true negatives, correctly identified as such) and for distinguishing TB from other diseases (sensitivity 93% and specificity 88%). In the independent validation cohort, the researchers found that patients with TB could be distinguished from patients with latent TB infection (sensitivity 95% and specificity 94%) and also from patients with other diseases (sensitivity 100% and specificity 96%).
What Do These Findings Mean?
These findings suggest that a distinctive set of RNA transcriptional signatures forming a disease risk score might provide the basis of a diagnostic test that can distinguish active TB from latent TB infection (27 signatures) and also from other diseases (44 signatures), such as pneumonia, that are prevalent in African populations. There is a concern that using transcriptional signatures as a clinical diagnostic tool in resource poor settings might not be feasible because they are complex and costly. The relatively small number of transcripts in the signatures described here may increase the potential for using this approach (transcriptional profiling) as a clinical diagnostic tool using a single blood test. In order to make most use of these findings, there is an urgent need for the academic research community and for industry to develop innovative methods to translate multi-transcript signatures into simple, cheap tests for TB suitable for use in African health facilities.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/ 10.1371/journal.pmed.1001538.
Wikipedia has definitions of tests for gene expression (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
The National Center for Biotechnology Information has a fact sheet on microarray analysis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
The World Health Organization has up-to-date information on TB
The Stop TB partnership is working towards tuberculosis elimination; patient stories about tuberculosis/HIV coinfection are available
doi:10.1371/journal.pmed.1001538
PMCID: PMC3805485  PMID: 24167453
18.  Commercial Serological Tests for the Diagnosis of Active Pulmonary and Extrapulmonary Tuberculosis: An Updated Systematic Review and Meta-Analysis 
PLoS Medicine  2011;8(8):e1001062.
An up-to-date systematic review and meta-analysis by Karen Steingart and colleagues confirms that commercially available serological tests do not provide an accurate diagnosis of tuberculosis.
Background
Serological (antibody detection) tests for tuberculosis (TB) are widely used in developing countries. As part of a World Health Organization policy process, we performed an updated systematic review to assess the diagnostic accuracy of commercial serological tests for pulmonary and extrapulmonary TB with a focus on the relevance of these tests in low- and middle-income countries.
Methods and Findings
We used methods recommended by the Cochrane Collaboration and GRADE approach for rating quality of evidence. In a previous review, we searched multiple databases for papers published from 1 January 1990 to 30 May 2006, and in this update, we add additional papers published from that period until 29 June 2010. We prespecified subgroups to address heterogeneity and summarized test performance using bivariate random effects meta-analysis. For pulmonary TB, we included 67 studies (48% from low- and middle-income countries) with 5,147 participants. For all tests, estimates were variable for sensitivity (0% to 100%) and specificity (31% to 100%). For anda-TB IgG, the only test with enough studies for meta-analysis, pooled sensitivity was 76% (95% CI 63%–87%) in smear-positive (seven studies) and 59% (95% CI 10%–96%) in smear-negative (four studies) patients; pooled specificities were 92% (95% CI 74%–98%) and 91% (95% CI 79%–96%), respectively. Compared with ELISA (pooled sensitivity 60% [95% CI 6%–65%]; pooled specificity 98% [95% CI 96%–99%]), immunochromatographic tests yielded lower pooled sensitivity (53%, 95% CI 42%–64%) and comparable pooled specificity (98%, 95% CI 94%–99%). For extrapulmonary TB, we included 25 studies (40% from low- and middle-income countries) with 1,809 participants. For all tests, estimates were variable for sensitivity (0% to 100%) and specificity (59% to 100%). Overall, quality of evidence was graded very low for studies of pulmonary and extrapulmonary TB.
Conclusions
Despite expansion of the literature since 2006, commercial serological tests continue to produce inconsistent and imprecise estimates of sensitivity and specificity. Quality of evidence remains very low. These data informed a recently published World Health Organization policy statement against serological tests.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Every year nearly 10 million people develop tuberculosis—a contagious bacterial infection—and about two million people die from the disease. Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is spread in airborne droplets when people with the disease cough or sneeze. It usually infects the lungs (pulmonary tuberculosis) but can also infect the lymph nodes, bones, and other tissues (extrapulmonary tuberculosis). The characteristic symptoms of tuberculosis are a persistent cough, weight loss, and night sweats. Diagnostic tests for the disease include microscopic examination of sputum (mucus brought up from the lungs by coughing) for M. tuberculosis bacilli, chest radiography, mycobacterial culture (in which bacteriologists try to grow M. tuberculosis from sputum or tissue samples), and nucleic acid amplification tests (which detect the bacterium's genome in patient samples). Tuberculosis can usually be cured by taking several powerful drugs daily or several times a week for at least six months.
Why Was This Study Done?
Although efforts to control tuberculosis have advanced over the past decade, missed tuberculosis diagnoses and mismanaged tuberculosis continue to fuel the global epidemic. A missed diagnosis may lead to more severe illness and death, especially for people infected with both tuberculosis and HIV. Also, a missed diagnosis means that an untreated individual with pulmonary tuberculosis may remain infectious for longer, continuing to spread tuberculosis within the community Missed diagnoses are a particular problem in resource-limited countries where sputum microscopy and chest radiography often perform poorly and other diagnostic tests are too expensive and complex for routine use. Serological tests, which detect antibodies against M. tuberculosis in the blood (antibodies are proteins made by the immune system in response to infections), might provide a way to diagnose tuberculosis in resource-limited countries. Indeed, many serological tests for tuberculosis diagnosis are on sale in developing countries. However, because of doubts about the accuracy of these commercial tests, they are not recommended for use in routine practice. In this systematic review and meta-analysis, the researchers assess the diagnostic accuracy of commercial serological tests for pulmonary and extrapulmonary tuberculosis. A systematic review uses predefined criteria to identify all the research on a given topic; meta-analysis is a statistical method that combines the results of several studies.
What Did the Researchers Do and Find?
The researchers searched the literature for studies that evaluated serological tests for active tuberculosis published between 1990 and 2010. They used data from these studies to calculate each test's sensitivity (the proportion of patients with a positive serological test among patients with tuberculosis confirmed by a reference method; a high sensitivity indicates that the test detects most patients with tuberculosis) and specificity (the proportion of patients with a negative serological result among people without tuberculosis; a high specificity means the test gives few false-positive diagnoses). They also assessed the methodological quality of each study and rated the overall quality of the evidence. The researchers found 67 studies (half from low/middle-income countries) that evaluated serological tests for the diagnosis of pulmonary tuberculosis. The sensitivity of these tests varied between studies, ranging from 0% to 100%; their specificities ranged from 31% to 100%. For the anda-TB IgG test—the only test with sufficient studies for a meta-analysis—the pooled sensitivity from the relevant studies was 76% in smear-positive patients and 59% in smear-negative patients. The pooled specificities were 92% and 91%, respectively. The researchers found 25 studies (40% from low/middle-income countries) that evaluated serological tests for the diagnosis of extrapulmonary tuberculosis. Again, sensitivities and specificities for each test varied greatly between studies, ranging from 0% to 100% and 59% to 100%, respectively. Overall, for both pulmonary and extrapulmonary tuberculosis, the quality of evidence from the studies of the serological tests was graded very low.
What Do These Findings Mean?
This systematic review, which updates an analysis published in 2007, indicates that commercial serological tests do not provide an accurate diagnosis of tuberculosis. This finding confirms previous systematic reviews of the evidence, despite a recent expansion in the relevant literature. Moreover, the researchers' analysis indicates that the overall quality of the body of evidence on these tests remains poor. Many of the identified studies used unsatisfactory patient selection methods, for example. Clearly, there is a need for continued and improved research on existing serological tests and for research into new approaches to the serological diagnosis of tuberculosis. For now, though, based on these findings, cost-effectiveness data, and expert opinion, the World Health Organization has issued a recommendation against the use of currently available serological tests for the diagnosis of tuberculosis, while stressing the importance of continued research on these and other tests that could provide quick and accurate diagnosis of TB.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001062.
The World Health Organization provides information on all aspects of tuberculosis, including information on tuberculosis diagnostics on the Stop TB Partnership (some information is in several languages); the Strategic and Technical Advisory Group for Tuberculosis recommendations on tuberculosis diagnosis are available
The Web site Evidence-Based Tuberculosis Diagnosis (from Stop TB Partnership's New Diagnostics Working Group) provides access to several resources on TB diagnostics, including systematic reviews, guidelines, and training materials
The US Centers for Disease Control and Prevention has information about tuberculosis, including information on the diagnosis of tuberculosis disease
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001062
PMCID: PMC3153457  PMID: 21857806
19.  Population Health Impact and Cost-Effectiveness of Tuberculosis Diagnosis with Xpert MTB/RIF: A Dynamic Simulation and Economic Evaluation 
PLoS Medicine  2012;9(11):e1001347.
Nicolas Menzies and colleagues investigate the potential impact and cost-effectiveness of implementing Xpert MTB/RIF for diagnosing tuberculosis in five southern African countries.
Background
The Xpert MTB/RIF test enables rapid detection of tuberculosis (TB) and rifampicin resistance. The World Health Organization recommends Xpert for initial diagnosis in individuals suspected of having multidrug-resistant TB (MDR-TB) or HIV-associated TB, and many countries are moving quickly toward adopting Xpert. As roll-out proceeds, it is essential to understand the potential health impact and cost-effectiveness of diagnostic strategies based on Xpert.
Methods and Findings
We evaluated potential health and economic consequences of implementing Xpert in five southern African countries—Botswana, Lesotho, Namibia, South Africa, and Swaziland—where drug resistance and TB-HIV coinfection are prevalent. Using a calibrated, dynamic mathematical model, we compared the status quo diagnostic algorithm, emphasizing sputum smear, against an algorithm incorporating Xpert for initial diagnosis. Results were projected over 10- and 20-y time periods starting from 2012. Compared to status quo, implementation of Xpert would avert 132,000 (95% CI: 55,000–284,000) TB cases and 182,000 (97,000–302,000) TB deaths in southern Africa over the 10 y following introduction, and would reduce prevalence by 28% (14%–40%) by 2022, with more modest reductions in incidence. Health system costs are projected to increase substantially with Xpert, by US$460 million (294–699 million) over 10 y. Antiretroviral therapy for HIV represents a substantial fraction of these additional costs, because of improved survival in TB/HIV-infected populations through better TB case-finding and treatment. Costs for treating MDR-TB are also expected to rise significantly with Xpert scale-up. Relative to status quo, Xpert has an estimated cost-effectiveness of US$959 (633–1,485) per disability-adjusted life-year averted over 10 y. Across countries, cost-effectiveness ratios ranged from US$792 (482–1,785) in Swaziland to US$1,257 (767–2,276) in Botswana. Assessing outcomes over a 10-y period focuses on the near-term consequences of Xpert adoption, but the cost-effectiveness results are conservative, with cost-effectiveness ratios assessed over a 20-y time horizon approximately 20% lower than the 10-y values.
Conclusions
Introduction of Xpert could substantially change TB morbidity and mortality through improved case-finding and treatment, with more limited impact on long-term transmission dynamics. Despite extant uncertainty about TB natural history and intervention impact in southern Africa, adoption of Xpert evidently offers reasonable value for its cost, based on conventional benchmarks for cost-effectiveness. However, the additional financial burden would be substantial, including significant increases in costs for treating HIV and MDR-TB. Given the fundamental influence of HIV on TB dynamics and intervention costs, care should be taken when interpreting the results of this analysis outside of settings with high HIV prevalence.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
In 2010, about 9 million people developed tuberculosis (TB)—a contagious bacterial disease that usually infects the lungs—and about 1.5 million people died from the disease. Most of these deaths were in low- and middle-income countries, and a quarter were in HIV-positive individuals, who are particularly susceptible to TB. Mycobacterium tuberculosis, the bacterium that causes TB, is spread in airborne droplets when people with active disease cough or sneeze. The characteristic symptoms of TB are a persistent cough, weight loss, fever, and night sweats. Diagnostic tests for TB include sputum smear analysis (microscopic examination of mucus coughed up from the lungs for the presence of M. tuberculosis) and mycobacterial liquid culture (growth of M. tuberculosis from sputum and determination of its drug sensitivity). TB can be cured by taking several antibiotics daily for at least six months, although the recent emergence of multidrug-resistant TB (MDR-TB) is making the disease increasingly hard to treat.
Why Was This Study Done?
To reduce the global TB burden, active disease must be diagnosed quickly and accurately. In most high-burden settings, however, TB diagnosis relies on sputum smear analysis, which fails to identify some people (especially HIV-infected individuals) who have TB. Mycobacterial culture correctly identifies more infected people but is slow and costly, and many high-burden settings lack the infrastructure for high-volume culture diagnosis of TB. Faced with these diagnostic inadequacies, the World Health Organization (WHO) recently recommended the use of Xpert MTB/RIF for initial diagnosis in patients suspected of having MDR-TB or HIV-associated TB. This new, automated DNA test detects M. tuberculosis and DNA differences that make the bacteria resistant to the drug rifampicin (an indicator of MDR-TB) within two hours. Many countries are moving toward adopting Xpert for TB diagnosis, so it is essential to understand the population health impact and cost-effectiveness of diagnostic strategies based on this test. Here, the researchers use a calibrated, dynamic mathematical model of TB to investigate the consequences of Xpert MTB/RIF implementation in five southern African countries where both TB-HIV coinfection and MDR-TB are common.
What Did the Researchers Do and Find?
The researchers used their mathematical model, which simulates the movement of individuals through different stages of TB infection, to investigate the potential health and economic consequences of implementing Xpert for initial TB diagnosis in Botswana, Lesotho, Namibia, South Africa, and Swaziland. In the modeled scenarios, compared to an diagnostic approach based on sputum smear (the “status quo”), implementation of Xpert averted an estimated 132,000 TB cases and 182,000 TB deaths in southern Africa over the ten years following its introduction, reduced the proportion of the population with TB by 28%, and increased health service costs by US$460 million. Much of this cost increase reflected increased antiretroviral therapy costs for TB/HIV-infected individuals who survived TB infection because of better case-finding and treatment. Finally, relative to the status quo, over ten years, Xpert implementation in southern Africa cost US$959 for every DALY (disability-adjusted life-year) averted. Cost-effectiveness ratios in individual countries ranged from US$792 per DALY averted in Swaziland to US$1,257 per DALY averted in Botswana.
What Do These Findings Mean?
These findings suggest that Xpert implementation in southern Africa could substantially reduce TB illness and death through improved case-finding and treatment, but that the impact of Xpert on long-term transmission dynamics may be more limited. Although the additional financial burden associated with Xpert roll-out is likely to be substantial, these findings suggest that using Xpert for TB diagnosis offers reasonable value given its cost. WHO considers any intervention with a cost-effectiveness ratio less than the per-capita gross domestic product (GDP) highly cost-effective—in 2010, the per-capita GDP ranged from US$7,000 in South Africa and Botswana to US$982 in Lesotho.
These findings may not be generalizable to regions with different HIV infection rates, and their accuracy is likely to be affected by the quality of the data fed into the mathematical model and by the structure of the model. Thus, it is essential that the impact of Xpert-based TB diagnosis be carefully evaluated as the approach is rolled out, and that the information generated by these evaluations be used to improve the accuracy of model-based estimates of the long-term effects of this new strategy for TB diagnosis.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001347.
WHO provides information (in several languages) on all aspects of tuberculosis, including general information on tuberculosis diagnostics and specific information on the roll-out of the Xpert MTB/RIF test; further information about WHO's endorsement of Xpert MTB/RIF is included in a recent Strategic and Technical Advisory Group for Tuberculosis report; WHO also provides information about tuberculosis and HIV
The Stop TB Partnership is working towards tuberculosis elimination; patient stories about TB-HIV coinfection are available
The US Centers for Disease Control and Prevention has information about tuberculosis, and about TB diagnosis
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
The Tuberculosis Survival Project, which aims to raise awareness of tuberculosis and provide support for people with tuberculosis, provides personal stories about treatment for tuberculosis; the Tuberculosis Vaccine Initiative also provides personal stories about dealing with tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001347
PMCID: PMC3502465  PMID: 23185139
20.  Evaluation of the 2007 WHO Guideline to Improve the Diagnosis of Tuberculosis in Ambulatory HIV-Positive Adults 
PLoS ONE  2011;6(4):e18502.
Background
In 2007 WHO issued a guideline to improve the diagnosis of smear-negative and extrapulmonary tuberculosis (EPTB) in HIV-positive patients. This guideline relies heavily on the acceptance of HIV-testing and availability of chest X-rays.
Methods and Findings
Cohort study of TB suspects in four tuberculosis (TB) clinics in Phnom Penh, Cambodia. We assessed the operational performance of the guideline, the incremental yield of investigations, and the diagnostic accuracy for smear-negative tuberculosis in HIV-positive patients using culture positivity as reference standard. 1,147 (68.9%) of 1,665 TB suspects presented with unknown HIV status, 1,124 (98.0%) agreed to be tested, 79 (7.0%) were HIV-positive. Compliance with the guideline for chest X-rays and sputum culture requests was 97.1% and 98.3% respectively. Only 35 of 79 HIV-positive patients (44.3%) with a chest X-ray suggestive of TB started TB treatment within 10 days. 105 of 442 HIV-positive TB suspects started TB treatment (56.2% smear-negative pulmonary TB (PTB), 28.6% smear-positive PTB, 15.2% EPTB). The median time to TB treatment initiation was 5 days (IQR: 2–13 days), ranging from 2 days (IQR: 1–11.5 days) for EPTB, over 2.5 days (IQR: 1–4 days) for smear-positive PTB to 9 days (IQR: 3–17 days) for smear-negative PTB. Among the 34 smear-negative TB patients with a confirmed diagnosis, the incremental yield of chest X-ray, clinical suspicion or abdominal ultrasound, and culture was 41.2%, 17.6% and 41.2% respectively. The sensitivity and specificity of the algorithm to diagnose smear-negative TB in HIV-positive TB suspects was 58.8% (95%CI: 42.2%–73.6%) and 79.4% (95%CI: 74.8%–82.4%) respectively.
Conclusions
Pending point-of-care rapid diagnostic tests for TB disease, diagnostic algorithms are needed. The diagnostic accuracy of the 2007 WHO guideline to diagnose smear-negative TB is acceptable. There is, however, reluctance to comply with the guideline in terms of immediate treatment initiation.
doi:10.1371/journal.pone.0018502
PMCID: PMC3071837  PMID: 21494694
21.  An Early Morning Sputum Sample Is Necessary for the Diagnosis of Pulmonary Tuberculosis, Even with More Sensitive Techniques: A Prospective Cohort Study among Adolescent TB-Suspects in Uganda 
The World Health Organization (WHO) recommends collection of two sputum samples for tuberculosis (TB) diagnosis, with at least one being an early morning (EM) using smear microscopy. It remains unclear whether this is necessary even when sputum culture is employed. Here, we determined the diagnostic yield from spot and the incremental yield from the EM sputum sample cultures among TB-suspected adolescents from rural Uganda. Sputum samples (both spot and early-morning) from 1862 adolescents were cultured by the Lowenstein-Jensen (LJ) and Mycobacterium Growth Indicator Tube (MGIT) methods. For spot samples, the diagnostic yields for TB were 19.0% and 57.1% with LJ and MGIT, respectively, whereas the incremental yields (not totals) of the early-morning sample were 9.5% and 42.9% (P < 0.001) with LJ and MGIT, respectively. Among TB-suspected adolescents in rural Uganda, the EM sputum culture has a high incremental diagnostic yield. Therefore, EM sputum in addition to spot sample culture is necessary for improved TB case detection.
doi:10.1155/2012/970203
PMCID: PMC3529437  PMID: 23304491
22.  Clinical Utility of a Novel Molecular Assay in Various Combination Strategies with Existing Methods for Diagnosis of HIV-Related Tuberculosis in Uganda 
PLoS ONE  2014;9(9):e107595.
Background
Low income, high-tuberculosis burden, countries are considering selective deployment of Xpert MTB/RIF assay (Xpert) due to high cost per test. We compared the diagnostic gain of the Xpert add-on strategy with Xpert replacement strategy for pulmonary tuberculosis diagnosis among HIV-infected adults to inform its implementation.
Methods
The first diagnostic sputum sample of 424 HIV-infected adults (67% with CD4 counts ≤200/mm3) suspected for tuberculosis was tested by direct Ziehl-Neelsen (DZN) and direct fluorescent microscopy (DFM); concentrated fluorescent microscopy (CFM); Lowenstein-Jensen (LJ) and Mycobacterial Growth Indicator Tube (MGIT) culture; and Xpert. Overall diagnostic yield and sensitivity were calculated using MGIT as reference comparator. The sensitivity of Xpert in an add-on strategy was calculated as the number of smear negative but Xpert positive participants among MGIT positive participants.
Results
A total of 123 (29.0%) participants were MGIT culture positive for Mycobacterium tuberculosis. The sensitivity (95% confidence interval) was 31.7% (23.6–40.7%) for DZN, 35.0% (26.5–44.0%) for DFM, 43.9% (34.9–53.1%) for CFM, 76.4% (67.9–83.6) for Xpert and 81.3% (73.2–87.7%) for LJ culture. Add-on strategy Xpert showed an incremental sensitivity of 44.7% (35.7–53.9%) when added to DZN, 42.3% (33.4–51.5%) to DFM and 35.0% (26.5–44.0%) to CFM. This translated to an overall sensitivity of 76.4%, 77.3% and 79.0% for add-on strategies based on DZN, DFM and CFM, respectively, compared to 76.4% for Xpert done independently. From replacement to add-on strategy, the number of Xpert cartridges needed was reduced by approximately 10%.
Conclusions
Among HIV-infected TB suspects, doing smear microscopy prior to Xpert assay in add-on fashion only identifies a few additional TB cases.
doi:10.1371/journal.pone.0107595
PMCID: PMC4164637  PMID: 25222866
23.  A Multi-Country Non-Inferiority Cluster Randomized Trial of Frontloaded Smear Microscopy for the Diagnosis of Pulmonary Tuberculosis 
PLoS Medicine  2011;8(7):e1000443.
Luis Cuevas and colleagues report findings from a multicenter diagnostic clinical trial in tuberculosis, showing that the sensitivity and specificity of a “front-loaded” diagnostic scheme is not inferior to that of a standard diagnostic scheme.
Background
More than 50 million people around the world are investigated for tuberculosis using sputum smear microscopy annually. This process requires repeated visits and patients often drop out.
Methods and Findings
This clinical trial of adults with cough ≥2 wk duration (in Ethiopia, Nepal, Nigeria, and Yemen) compared the sensitivity/specificity of two sputum samples collected “on the spot” during the first visit plus one sputum sample collected the following morning (spot-spot-morning [SSM]) versus the standard spot-morning-spot (SMS) scheme. Analyses were per protocol analysis (PPA) and intention to treat (ITT). A sub-analysis compared just the first two smears of each scheme, spot-spot and spot-morning.
In total, 6,627 patients (3,052 SSM/3,575 SMS) were enrolled; 6,466 had culture and 1,526 were culture-positive. The sensitivity of SSM (ITT, 70.2%, 95% CI 66.5%–73.9%) was non-inferior to the sensitivity of SMS (PPA, 65.9%, 95% CI 62.3%–69.5%). Similarly, the specificity of SSM (ITT, 96.9%, 95% CI 93.2%–99.9%) was non-inferior to the specificity of SMS (ITT, 97.6%, 95% CI 94.0%–99.9%). The sensitivity of spot-spot (ITT, 63.6%, 95% CI 59.7%–67.5%) was also non-inferior to spot-morning (ITT, 64.8%, 95% CI 61.3%–68.3%), as the difference was within the selected −5% non-inferiority limit (difference ITT = 1.4%, 95% CI −3.7% to 6.6%). Patients screened using the SSM scheme were more likely to provide the first two specimens than patients screened with the SMS scheme (98% versus 94.2%, p<0.01). The PPA and ITT analysis resulted in similar results.
Conclusions
The sensitivity and specificity of SSM are non-inferior to those of SMS, with a higher proportion of patients submitting specimens. The scheme identifies most smear-positive patients on the first day of consultation.
Trial Registration
Current Controlled Trials ISRCTN53339491
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Every year, nearly 10 million people develop tuberculosis—a contagious bacterial infection that usually affects the lungs (pulmonary tuberculosis)—and about 1.7 million people die from the disease. Mycobacterium tuberculosis, which causes tuberculosis, is spread in airborne droplets when people with the disease cough or sneeze. Thus, to control tuberculosis, it is essential that infected individuals are rapidly identified and treated. The “gold standard” diagnostic test for tuberculosis is mycobacterial culture, in which laboratory staff try to grow M. tuberculosis from sputum (mucus brought up from the lungs by coughing). However, although this test is sensitive (it detects most patients with tuberculosis) and has a high specificity (a low rate of false-positive results), it is too slow to produce results and too complex for routine use in the low- and middle-income countries where tuberculosis mainly occurs. In these countries, patients are usually investigated using direct sputum smear microscopy, a cheaper but less sensitive test in which multiple sputum samples treated with the acid-fast Ziehl-Neelsen stain are examined for the presence of M. tuberculosis bacilli.
Why Was This Study Done?
In most national tuberculosis control programs, patients provide an “on the spot” specimen during their initial consultation, a specimen collected at home the next morning, and another on-the-spot specimen when they bring their morning specimen to the clinic (a “spot-morning-spot,” or SMS, collection scheme). Unfortunately, patients often fail to return with their morning sample. Furthermore, the examination of three samples strains the limited laboratory resources of developing countries. Based on several recent reviews, the World Health Organization recently recommended that only two samples need be examined, a policy change that reduces the laboratory workload but does not avoid the problems of collecting a morning sample and patient drop-out during the diagnostic process. In this non-inferiority, cluster randomized trial, the researchers compare the sensitivity and specificity of a spot-spot-morning (SSM; two on-the-spot specimens collected during the first clinic visit an hour apart, and a third specimen collected at home the next morning) scheme for tuberculosis diagnosis with those of the standard SMS scheme. A non-inferiority trial investigates whether an intervention is not worse than a control intervention; a cluster randomized trial randomly assigns groups of patients rather than individual patients to the test and control interventions.
What Did the Researchers Do and Find?
The researchers enrolled 6,627 patients in Ethiopia, Nepal, Nigeria, and Yemen who had had a cough for more than two weeks (a characteristic symptom of tuberculosis). A quarter of the patients had culture-positive tuberculosis. The centers participating in the study were randomly assigned each week for a year to use either the SMS or the SSM sample collection scheme. Compared to mycobacterial culture, the sensitivities of the SSM and SMS schemes were 70.2% and 65.9%, respectively, which indicates that the new scheme was non-inferior to the SMS scheme. Similarly, the specificity of SSM (96.9%) was non-inferior to that of SMS (97.6%). Importantly, the sensitivity of diagnosis using just the first two samples collected in the SSM scheme was also non-inferior to the sensitivity of diagnosis using the first two samples collected in the SMS scheme (63.6% versus 64.8%; the researchers defined non-inferiority of SSM as a difference in its sensitivity compared to that of SMS of less than −5%). Finally, patients tested using the SSM scheme were more likely to provide the first two samples than patients tested using the SMS scheme (98% versus 94.2%).
What Do These Findings Mean?
These findings suggest that a sputum collection scheme in which two samples are collected one hour apart followed by a morning specimen could identify as many smear-positive patients as the standard SMS scheme. Importantly, they also indicate that examination of the first two specimens alone identifies most smear-positive patients independently of which scheme is used. These findings suggest that the SSM scheme might be more suitable for tuberculosis diagnosis than the SMS scheme in locations where patients are likely to drop out of the diagnosis process (for example, in low- and middle-income countries, where patients often live a long way from clinics). However, for an SSM scheme to work effectively, an on-site laboratory with a same-day turn-around service will be essential, and tuberculosis clinics will need to minimize contact between patients waiting to provide their second on-the-spot specimen.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000443.
A related PLoS Medicine Research Article by Cuevas et al. uses LED fluorescence microscopy for the diagnosis of pulmonary tuberculosis
The World Health Organization provides information on all aspects of tuberculosis, including information on tuberculosis diagnostics and on the recommendation to reduce the number of smears for diagnosis to two; the Stop TB Partnership provides information on global tuberculosis control (some information in several languages)
The US Centers for Disease Control and Prevention has information about tuberculosis, including information on the diagnosis of tuberculosis disease
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
A new Web site dedicated to the discussion and optimization of smear microscopy has recently been launched
doi:10.1371/journal.pmed.1000443
PMCID: PMC3134460  PMID: 21765808
24.  The Importance of Implementation Strategy in Scaling Up Xpert MTB/RIF for Diagnosis of Tuberculosis in the Indian Health-Care System: A Transmission Model 
PLoS Medicine  2014;11(7):e1001674.
Using a modelling approach, David Dowdy and colleagues investigate how different implementation strategies for Xpert MTB/RIF within the complex, fragmented healthcare system of India may affect tuberculosis control.
Please see later in the article for the Editors' Summary
Background
India has announced a goal of universal access to quality tuberculosis (TB) diagnosis and treatment. A number of novel diagnostics could help meet this important goal. The rollout of one such diagnostic, Xpert MTB/RIF (Xpert) is being considered, but if Xpert is used mainly for people with HIV or high risk of multidrug-resistant TB (MDR-TB) in the public sector, population-level impact may be limited.
Methods and Findings
We developed a model of TB transmission, care-seeking behavior, and diagnostic/treatment practices in India and explored the impact of six different rollout strategies. Providing Xpert to 40% of public-sector patients with HIV or prior TB treatment (similar to current national strategy) reduced TB incidence by 0.2% (95% uncertainty range [UR]: −1.4%, 1.7%) and MDR-TB incidence by 2.4% (95% UR: −5.2%, 9.1%) relative to existing practice but required 2,500 additional MDR-TB treatments and 60 four-module GeneXpert systems at maximum capacity. Further including 20% of unselected symptomatic individuals in the public sector required 700 systems and reduced incidence by 2.1% (95% UR: 0.5%, 3.9%); a similar approach involving qualified private providers (providers who have received at least some training in allopathic or non-allopathic medicine) reduced incidence by 6.0% (95% UR: 3.9%, 7.9%) with similar resource outlay, but only if high treatment success was assured. Engaging 20% of all private-sector providers (qualified and informal [providers with no formal medical training]) had the greatest impact (14.1% reduction, 95% UR: 10.6%, 16.9%), but required >2,200 systems and reliable treatment referral. Improving referrals from informal providers for smear-based diagnosis in the public sector (without Xpert rollout) had substantially greater impact (6.3% reduction) than Xpert scale-up within the public sector. These findings are subject to substantial uncertainty regarding private-sector treatment patterns, patient care-seeking behavior, symptoms, and infectiousness over time; these uncertainties should be addressed by future research.
Conclusions
The impact of new diagnostics for TB control in India depends on implementation within the complex, fragmented health-care system. Transformative strategies will require private/informal-sector engagement, adequate referral systems, improved treatment quality, and substantial resources.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Tuberculosis—a contagious bacterial disease that usually infects the lungs—is a global public health problem. Each year, about 8.7 million people develop active tuberculosis and about 1.4 million people die from the disease. Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is spread in airborne droplets when people with active disease cough or sneeze. The characteristic symptoms of tuberculosis are a persistent cough, fever, weight loss, and night sweats. Diagnostic tests for tuberculosis include sputum smear microscopy (microscopic analysis of mucus coughed up from the lungs), the growth of M. tuberculosis from sputum samples, and new molecular tests (for example, the automated Xpert MTB/RIF test) that rapidly and accurately detect M. tuberculosis in patient samples and determine its resistance to certain antibiotics. Tuberculosis can be cured by taking several antibiotics daily for at least six months, although the recent emergence of multidrug-resistant (MDR) tuberculosis is making the disease increasingly hard to treat.
Why Was This Study Done?
About 25% of all tuberculosis cases occur in India. Most people in India with underlying tuberculosis initially seek care for cough from the private health-care sector, which comprises informal providers with no formal medical training and providers with some training in mainstream or alternative medicine. Private providers rarely investigate for tuberculosis, and patients often move between providers, with long diagnostic delays. The public sector ultimately diagnoses and treats more than half of tuberculosis cases. However, the public sector relies on sputum smear microscopy, which misses half of cases, and the full diagnostic process from symptom onset to treatment initiation can take several months, during which time individuals remain infectious. Could the rollout of molecular diagnostic tests improve tuberculosis control in India? The Indian Revised National Tuberculosis Control Programme (RNTCP) is currently introducing the Xpert MTB/RIF test (Xpert) as a rapid method for drug susceptibility testing in the public sector in people at high risk of MDR tuberculosis, but is this the most effective rollout strategy? Here, the researchers use a mathematical transmission model to investigate the likely effects of the rollout of Xpert in India using different implementation strategies.
What Did the Researchers Do and Find?
The researchers explored the impact of several rollout strategies on the incidence of tuberculosis (the number of new cases of tuberculosis in the population per year) by developing a mathematical model of tuberculosis transmission, care-seeking behavior, and diagnostic/treatment practices in India. Compared to a baseline scenario of no improved diagnostic testing, provision of Xpert to 40% of public-sector patients at high risk of MDR tuberculosis (scenario 1, the current national strategy) reduced the incidence of tuberculosis by 0.2% and the incidence of MDR tuberculosis by 2.4%. Implementation of this strategy required 2,500 additional courses of MDR tuberculosis treatment and the continuous use of 60 Xpert machines, about half the machines procured in India during 2013. A scenario that added access to Xpert for 20% of all individuals with tuberculosis symptoms seeking diagnosis in the public sector and 20% of individuals seeking care from qualified private practitioners to scenario 1 reduced the incidence of tuberculosis by 14.1% compared to the baseline scenario but required more than 2,200 Xpert machines and reliable treatment referral. Notably, a scenario that encouraged informal providers to refer suspected tuberculosis cases to the public sector for smear-based diagnosis (no Xpert rollout) had a greater impact on the incidence of tuberculosis than Xpert scale-up within the public sector.
What Do These Findings Mean?
These findings are subject to considerable uncertainty because of the assumptions made in the transmission model about private-sector treatment patterns, patient care-seeking behavior, and infectiousness, and the quality of the data fed into the model. Nevertheless, these findings suggest that the rollout of Xpert (or other new diagnostic methods with similar characteristics) could substantially reduce the burden of tuberculosis due to poor diagnosis in India. Importantly, these findings highlight how the impact of Xpert rollout relies not only on the accuracy of the test but also on the behavior of patients and providers, the level of access to new tools, and the availability of treatment following diagnosis. Thus, to ensure that new diagnostic methods have the maximum impact on tuberculosis in India, it is necessary to engage the whole private health-care sector and to provide adequate referral systems, improved treatment quality, and increased resources across all health-care sectors.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001674.
The World Health Organization (WHO) provides information (in several languages) on all aspects of tuberculosis, including general information on tuberculosis diagnostics and specific information on the roll out of the Xpert MTB/RIF test; further information about WHO's endorsement of Xpert MTB/RIF is included in a Strategic and Technical Advisory Group for Tuberculosis report; the Global Tuberculosis Report 2013 provides information about tuberculosis around the world, including in India
The Stop TB Partnership is working towards tuberculosis elimination and provides patient stories about tuberculosis (in English and Spanish); the Tuberculosis Vaccine Initiative (a not-for-profit organization) also provides personal stories about tuberculosis
The US Centers for Disease Control and Prevention has information about tuberculosis and its diagnosis (in English and Spanish)
The US National Institute of Allergy and Infectious Diseases also has detailed information on all aspects of tuberculosis
TBC India provides information about tuberculosis control in India, including information on the RNTCP
The Initiative for Promoting Affordable and Quality TB Tests promotes WHO-endorsed TB tests in India
MedlinePlus has links to further information about tuberculosis (in English and Spanish)
doi:10.1371/journal.pmed.1001674
PMCID: PMC4098913  PMID: 25025235
25.  Incremental Yield of Serial Sputum Cultures for Diagnosis of Tuberculosis among HIV Infected Smear Negative Pulmonary TB Suspects in Kampala, Uganda 
PLoS ONE  2012;7(5):e37650.
Background
Sputum culture is the gold standard for diagnosis of pulmonary tuberculosis (PTB). Although mostly used for research, culture is recommended by the World Health Organization for TB diagnosis among HIV infected smear negative PTB suspects. Even then, the number of sputum samples required remains unspecified. Here, we determined the Incremental Yield (IY) and number of samples required to diagnose an additional PTB case upon second and third serial sputum culture.
Methods/Findings
This was a cross sectional study done between January and March 2011. Serial sputum samples were provided by participants within two days and cultured using Lowenstein Jensen (LJ) and Mycobacteria Growth Indicator Tube (MGIT) methods. A PTB case was defined as a positive culture on either one or both methods. The IY from the second and third serial cultures was determined and the reciprocal of the product of the fractions of IY provided the number of samples required for an additional PTB case. Of the 170 smear negative PTB suspects, 62 (36.5%) met the case definition. The IY of the second sample culture was 12.7%, 23.6% and 12.6% and for the third sample culture was 6.8%, 7.5% and 7.3% with LJ, MGIT and LJ or MGIT, respectively. The number of samples required for an additional PTB case and 95% CI upon the second sample culture were 29.9 (16.6, 156.5), 11.3 (7.6, 21.9) and 20.8 (12.5, 62.7); while for the third sample culture were 55.6 (26.4, 500.4), 35.7 (19.0, 313.8) and 36.1 (19.1, 330.9) by LJ, MGIT and LJ or MGIT respectively.
Conclusions/Significance
Among HIV infected smear negative PTB suspects in Kampala, 93% of PTB cases are diagnosed upon the second serial sputum culture. The number of cultures needed to diagnose an additional PTB case, ranges from 11–30 and 35–56 by the second and third sputum samples, respectively.
doi:10.1371/journal.pone.0037650
PMCID: PMC3358271  PMID: 22629439

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