Search tips
Search criteria

Results 1-22 (22)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
Document Types
author:("Fang, wicky J")
1.  Impact of live poultry market closure in reducing bird-to-human transmission of avian influenza A(H7N9) virus: an ecological study 
Lancet  2013;383(9916):541-548.
A novel influenza A(H7N9) virus has emerged in China during the past few months. Inter-species zoonotic transmission appears to be the predominant route of spread. Live poultry markets (LPMs) in the major cities of Shanghai, Hangzhou, Huzhou and Nanjing, where the majority of cases have occurred, were swiftly closed as a precautionary public health measure. Our objective was to quantify the impact of LPM closure in reducing bird-to-human transmission of avian influenza A(H7N9) virus.
We used data on the illness onset dates and geographical locations of laboratory-confirmed influenza A(H7N9) cases that were officially announced by 7 June 2013. We constructed a statistical model to explain the patterns in incident cases reported in each city based on the assumption of a constant force of infection prior to closure, and a different constant force of infection after closure. We fitted the model using Markov chain Monte Carlo methods.
There were 85 confirmed influenza A(H7N9) cases in Shanghai, Hangzhou, Huzhou and Nanjing out of a total of 130 confirmed cases in mainland China by 7 June 2013. Closure of LPMs in those four cities reduced the risk of human infections by 97%–99% (range 68%–100%) in each city. Given that LPMs were the predominant source of influenza A(H7N9) exposure in those locations, we estimated the mean incubation period to be 3.3 days.
LPM closures were extremely effective in controlling human risk of influenza A(H7N9). If the influenza A(H7N9) epizootic/epidemic continues, LPM closure should be sustained in at-risk areas and implemented in any urban areas where influenza A(H7N9) reappears in future. In the longer term, evidence-based discussions and deliberations about the role of central slaughtering of all live poultry should be renewed.
Ministry of Science and Technology, China; Research Fund for the Control of Infectious Disease and University Grants Committee, Hong Kong Special Administrative Region, China; and the US National Institutes of Health.
PMCID: PMC3946250  PMID: 24183056
2.  Poultry Market Closures and Human Infection with Influenza A(H7N9) Virus, China, 2013–14 
Emerging Infectious Diseases  2014;20(11):1891-1894.
Closure of live poultry markets was implemented in areas affected by the influenza virus A(H7N9) outbreak in China during winter, 2013–14. Our analysis showed that closing live poultry markets in the most affected cities of Guangdong and Zhejiang provinces was highly effective in reducing the risk for H7N9 infection in humans.
PMCID: PMC4214308  PMID: 25340354
Avian influenza A(H7N9); viruses; live poultry markets; public health; China
3.  Estimation of the Association Between Antibody Titers and Protection Against Confirmed Influenza Virus Infection in Children 
The Journal of Infectious Diseases  2013;208(8):1320-1324.
Antibody titers measured by hemagglutination inhibition (HAI) correlate with protection against influenza virus infection and are used to specify criteria for vaccine licensure. In a randomized, controlled trial of seasonal influenza vaccination in 773 children aged 6–17 years, we estimated that HAI titers of 1:40 against A(H1N1)pdm09 and B(Victoria lineage) were associated with 48% (95% confidence interval [CI], 30%–62%) and 55% (95% CI, 32%–70%) protection against PCR-confirmed infection with each strain. Our analysis accounted for waning in antibody titers over time, and could be particularly useful in settings where influenza activity is delayed or prolonged relative to measurement of antibody titers.
PMCID: PMC3778972  PMID: 23908481
antibody; immunity; influenza; vaccine; children
4.  Modes of Transmission of Influenza B Virus in Households 
PLoS ONE  2014;9(9):e108850.
While influenza A and B viruses can be transmitted via respiratory droplets, the importance of small droplet nuclei “aerosols” in transmission is controversial.
Methods and Findings
In Hong Kong and Bangkok, in 2008–11, subjects were recruited from outpatient clinics if they had recent onset of acute respiratory illness and none of their household contacts were ill. Following a positive rapid influenza diagnostic test result, subjects were randomly allocated to one of three household-based interventions: hand hygiene, hand hygiene plus face masks, and a control group. Index cases plus their household contacts were followed for 7–10 days to identify secondary infections by reverse transcription polymerase chain reaction (RT-PCR) testing of respiratory specimens. Index cases with RT-PCR-confirmed influenza B were included in the present analyses. We used a mathematical model to make inferences on the modes of transmission, facilitated by apparent differences in clinical presentation of secondary infections resulting from aerosol transmission. We estimated that approximately 37% and 26% of influenza B virus transmission was via the aerosol mode in households in Hong Kong and Bangkok, respectively. In the fitted model, influenza B virus infections were associated with a 56%–72% risk of fever plus cough if infected via aerosol route, and a 23%–31% risk of fever plus cough if infected via the other two modes of transmission.
Aerosol transmission may be an important mode of spread of influenza B virus. The point estimates of aerosol transmission were slightly lower for influenza B virus compared to previously published estimates for influenza A virus in both Hong Kong and Bangkok. Caution should be taken in interpreting these findings because of the multiple assumptions inherent in the model, including that there is limited biological evidence to date supporting a difference in the clinical features of influenza B virus infection by different modes.
PMCID: PMC4182555  PMID: 25268241
5.  Comparative epidemiology of human infections with avian influenza A(H7N9) and A(H5N1) viruses in China 
Lancet  2013;382(9887):129-137.
The novel influenza A(H7N9) virus recently emerged, while influenza A(H5N1) virus has infected humans since 2003 in mainland China. Both infections are thought to be predominantly zoonotic. We compared the epidemiologic characteristics of the complete series of laboratory-confirmed cases of both viruses in mainland China to date.
An integrated database was constructed with information on demographic, epidemiological, and clinical variables of laboratory-confirmed A(H7N9) and A(H5N1) cases that were reported to the Chinese Center for Disease Control and Prevention up to May 24, 2013. We described disease occurrence by age, sex and geography and estimated key epidemiologic parameters.
Among 130 and 43 patients with confirmed A(H7N9) and A(H5N1) respectively, the median ages were 62y and 26y. In urban areas, 74% of cases of both viruses were male whereas in rural areas the proportions were 62% for A(H7N9) and 33% for A(H5N1). Among cases of A(H7N9) and A(H5N1), 75% and 71% reported recent exposure to poultry. The mean incubation periods of A(H7N9) and A(H5N1) were 3.1 and 3.3 days, respectively. On average, 21 and 18 contacts were traced for each A(H7N9) case in urban and rural areas respectively; compared to 90 and 63 for A(H5N1). The hospitalization fatality risk was 35% (95% CI: 25%, 44%) for A(H7N9) and 70% (95% CI: 56%, 83%) for A(H5N1).
The sex ratios in urban compared to rural cases are consistent with poultry exposure driving the risk of infection. However the difference in susceptibility to serious illness with the two different viruses remains unexplained, given that most A(H7N9) cases were in older adults while most A(H5N1) cases were in younger individuals.
Ministry of Science and Technology, China; Research Fund for the Control of Infectious Disease and University Grants Committee, Hong Kong Special Administrative Region, China; and the US National Institutes of Health.
PMCID: PMC3777567  PMID: 23803488
6.  Clinical severity of human infection with avian influenza A(H7N9) virus 
Lancet  2013;382(9887):138-145.
Characterizing the severity profile of human infections with influenza viruses of animal origin is a part of pandemic risk assessment, and an important part of the assessment of disease epidemiology. Our objective was to assess the clinical severity of human infections with the avian influenza A(H7N9) virus that has recently emerged in China.
Among laboratory-confirmed cases of A(H7N9) who were hospitalised, we estimated the risk of fatality, mechanical ventilation, and admission to the intensive care unit based on censored data during the currently ongoing outbreak. We also used information on laboratory-confirmed cases detected through sentinel influenza-like illness (ILI) surveillance to estimate the number of symptomatic A(H7N9) virus infections to date and the symptomatic case fatality risk.
Among 123 hospitalised cases, 37 cases had died and 69 had recovered by May 28, 2013. Hospitalised cases had high risks of mortality (36%; 95% confidence interval (CI): 26%–45%), mechanical ventilation or mortality (69%; 95% CI: 60%–77%), and ICU admission or mechanical ventilation or mortality (83%; 95% CI: 76%–90%), and the risk of these severe outcomes increased with age. Depending on assumptions about the coverage of the sentinel ILI network and health-care seeking behavior for cases of ILI associated with A(H7N9) virus infection, we estimated that the symptomatic case fatality risk could be between 160 and 2,800 per 100,000 symptomatic cases.
We estimated that the severity of A(H7N9) is somewhat lower than A(H5N1) but higher than seasonal influenza viruses and influenza A(H1N1)pdm09 virus. The estimated risks of fatality among hospitalised cases and symptomatic cases are measures of severity that should not be affected by shifts over time in the probability of laboratory-confirmation of mild cases and should inform risk assessment.
Ministry of Science and Technology, China; Research Fund for the Control of Infectious Disease and University Grants Committee, Hong Kong Special Administrative Region, China; and the US National Institutes of Health.
PMCID: PMC3801178  PMID: 23803487
7.  Comparative Epidemiology of Pandemic and Seasonal Influenza A in Households 
The New England journal of medicine  2010;362(23):2175-2184.
There are few data on the comparative epidemiology and virology of the pandemic 2009 influenza A (H1N1) virus and cocirculating seasonal influenza A viruses in community settings.
We recruited 348 index patients with acute respiratory illness from 14 outpatient clinics in Hong Kong in July and August 2009. We then prospectively followed household members of 99 patients who tested positive for influenza A virus on rapid diagnostic testing. We collected nasal and throat swabs from all household members at three home visits within 7 days for testing by means of quantitative reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assay and viral culture. Using hemagglutination-inhibition and viral-neutralization assays, we tested baseline and convalescent serum samples from a subgroup of patients for antibody responses to the pandemic and seasonal influenza A viruses.
Secondary attack rates (as confirmed on RT-PCR assay) among household contacts of index patients were similar for the pandemic influenza virus (8%; 95% confidence interval [CI], 3 to 14) and seasonal influenza viruses (9%; 95% CI, 5 to 15). The patterns of viral shedding and the course of illness among index patients were also similar for the pandemic and seasonal influenza viruses. In a subgroup of patients for whom baseline and convalescent serum samples were available, 36% of household contacts who had serologic evidence of pandemic influenza virus infection did not shed detectable virus or report illness.
Pandemic 2009 H1N1 virus has characteristics that are broadly similar to those of seasonal influenza A viruses in terms of rates of viral shedding, clinical illness, and transmissibility in the household setting.
PMCID: PMC4070281  PMID: 20558368
8.  The Serial Intervals of Seasonal and Pandemic Influenza Viruses in Households in Bangkok, Thailand 
American Journal of Epidemiology  2013;177(12):1443-1451.
The serial interval (SI) of human influenza virus infections is often described by a single distribution. Understanding sources of variation in the SI could provide valuable information for understanding influenza transmission dynamics. Using data from a randomized household study of nonpharmaceutical interventions to prevent influenza transmission in Bangkok, Thailand, over 34 months between 2008 and 2011, we estimated the influence of influenza virus type/subtype and other characteristics of 251 pediatric index cases and their 315 infected household contacts on estimates of household SI. The mean SI for all households was 3.3 days. Relative to influenza A(H1N1)pdm09 (3.1 days), the SI for influenza B (3.7 days) was 22% longer (95% confidence interval: 4, 43), or about half a day. The SIs for influenza viruses A(H1N1) and A(H3N2) were similar to that for A(H1N1)pdm09. SIs were shortest for older index cases (age 11–14 years) and for younger infected household contacts (age ≤15 years). Greater time spent in proximity to the index child was associated with shorter SIs. Differences in the SI might reflect differences in incubation period, viral shedding, contact, or susceptibility. These findings could improve parameterization of mathematical models to better predict the impact of epidemic or pandemic influenza mitigation strategies.
PMCID: PMC3676150  PMID: 23629874
human; influenza; Thailand
9.  Responses to Threat of Influenza A(H7N9) and Support for Live Poultry Markets, Hong Kong, 2013 
Emerging Infectious Diseases  2014;20(5):882-886.
We conducted a population survey in Hong Kong to gauge psychological and behavioral responses to the threat of influenza A(H7N9) and support for closure of live poultry markets. We found low anxiety and low levels of exposure to live poultry but mixed support for permanent closure of the markets.
PMCID: PMC4012820  PMID: 24750988
avian influenza A(H7N9); influenza; viruses; Hong Kong; public health; behavioral response; psychological response; community; H7N9; survey; respiratory infections; live poultry markets; poultry; birds
10.  Heterogeneity in Viral Shedding Among Individuals With Medically Attended Influenza A Virus Infection 
The Journal of Infectious Diseases  2013;207(8):1281-1285.
Compared with the average transmissibility of human influenza A virus, much less attention has been paid to the potential variability in its transmissibility. We considered viral shedding as a proxy for infectiousness and explored the heterogeneity of infectiousness among patients with medically attended seasonal influenza A virus infection. The analysis revealed that viral shedding is more heterogeneous in children than in adults. The top 20% most infectious children and adults were estimated to be responsible for 89%–96% and 78%–82%, respectively, of the total infectiousness in each age group. Further investigation is required to correlate the substantial variations in viral shedding with heterogeneity in actual transmissibility.
PMCID: PMC3603536  PMID: 23382573
influenza; viral shedding; infectiousness
11.  Humoral Antibody Response after Receipt of Inactivated Seasonal Influenza Vaccinations one Year Apart in Children 
In a randomized controlled trial, we administered seasonal trivalent inactivated influenza vaccine (TIV) or placebo to subjects 6–15 years of age in two consecutive years. Receipt of TIV in year 2 induced seroprotection in most subjects. Among 39 children who received TIV in the second year, receipt of TIV in the first year was associated with lower antibody titer rises in the second year to seasonal influenza A(H1N1) and A(H3N2) strains for which the vaccine strains remained unchanged. Antibody response to a different influenza B strain in the second year was unaffected by receipt of TIV in the first year.
PMCID: PMC3422369  PMID: 22683675
vaccination; influenza; antibody response; children
12.  Aerosol transmission is an important mode of influenza A virus spread 
Nature communications  2013;4:1935.
Influenza A viruses are believed to spread between humans through contact, large respiratory droplets and small particle droplet nuclei (aerosols), but the relative importance of each of these modes of transmission is unclear. Volunteer studies suggest that infections via aerosol transmission may have a higher risk of febrile illness. Here we apply a mathematical model to data from randomized controlled trials of hand hygiene and surgical face masks in Hong Kong and Bangkok households. In these particular environments, inferences on the relative importance of modes of transmission are facilitated by information on the timing of secondary infections and apparent differences in clinical presentation of secondary infections resulting from aerosol transmission. We find that aerosol transmission accounts for approximately half of all transmission events. This implies that measures to reduce transmission by contact or large droplets may not be sufficient to control influenza A virus transmission in households.
PMCID: PMC3682679  PMID: 23736803
13.  Increased Risk of Noninfluenza Respiratory Virus Infections Associated With Receipt of Inactivated Influenza Vaccine 
We randomized 115 children to trivalent inactivated influenza vaccine (TIV) or placebo. Over the following 9 months, TIV recipients had an increased risk of virologically-confirmed non-influenza infections (relative risk: 4.40; 95% confidence interval: 1.31-14.8). Being protected against influenza, TIV recipients may lack temporary non-specific immunity that protected against other respiratory viruses.
PMCID: PMC3404712  PMID: 22423139
14.  The Effect of Age and Recent Influenza Vaccination History on the Immunogenicity and Efficacy of 2009–10 Seasonal Trivalent Inactivated Influenza Vaccination in Children 
PLoS ONE  2013;8(3):e59077.
There is some evidence that annual vaccination of trivalent inactivated influenza vaccine (TIV) may lead to reduced vaccine immunogenicity but evidence is lacking on whether vaccine efficacy is affected by prior vaccination history. The efficacy of one dose of TIV in children 6–8 y of age against influenza B is uncertain. We examined whether immunogenicity and efficacy of influenza vaccination in school-age children varied by age and past vaccination history.
Methods and Findings
We conducted a randomized controlled trial of 2009–10 TIV. Influenza vaccination history in the two preceding years was recorded. Immunogenicity was assessed by comparison of HI titers before and one month after receipt of TIV/placebo. Subjects were followed up for 11 months with symptom diaries, and respiratory specimens were collected during acute respiratory illnesses to permit confirmation of influenza virus infections. We found that previous vaccination was associated with reduced antibody responses to TIV against seasonal A(H1N1) and A(H3N2) particularly in children 9–17 y of age, but increased antibody responses to the same lineage of influenza B virus in children 6–8 y of age. Serological responses to the influenza A vaccine viruses were high regardless of vaccination history. One dose of TIV appeared to be efficacious against confirmed influenza B in children 6–8 y of age regardless of vaccination history.
Prior vaccination was associated with lower antibody titer rises following vaccination against seasonal influenza A vaccine viruses, but higher responses to influenza B among individuals primed with viruses from the same lineage in preceding years. In a year in which influenza B virus predominated, no impact of prior vaccination history was observed on vaccine efficacy against influenza B. The strains that circulated in the year of study did not allow us to study the effect of prior vaccination on vaccine efficacy against influenza A.
PMCID: PMC3595209  PMID: 23554974
15.  Validation of Self-swab for Virologic Confirmation of Influenza Virus Infections in a Community Setting 
The Journal of Infectious Diseases  2011;205(4):631-634.
Few studies have investigated the validity of self-collected nose and throat swabs for influenza confirmation in community settings. We followed outpatients with confirmed influenza with sequential measurement of viral loads and applied log-linear regression models to the viral shedding patterns. Among 176 outpatients with confirmed influenza, the detection of virus and quantitative viral loads obtained from self-swabs was consistent with statistical predictions based on earlier and later measurements, suggesting that self-collected nose and throat swabs can be a valid alternative for virologic confirmation of influenza A or B infection in a community setting.
PMCID: PMC3266138  PMID: 22198963
16.  Transmissibility of seasonal and pandemic influenza in a cohort of households in Hong Kong in 2009 
Epidemiology (Cambridge, Mass.)  2011;22(6):793-796.
The household secondary attack proportion is commonly used to measure the transmissibility of an infectious disease.
We analyzed the final outbreak distributions of pandemic A(H1N1), seasonal A(H1N1) and A(H3N2) infections identified in paired sera collected from members of 117 Hong Kong households in April and August-October 2009.
The estimated community probability of infection overall was higher for children than adults; the probability was similar for pandemic A(H1N1) and seasonal A(H3N2) influenza. The household secondary attack proportion for pandemic A(H1N1) was higher in children than adults, whereas for seasonal A(H3N2) it was similar in children and adults. The estimated secondary attack proportions were similar for seasonal A(H3N2) and pandemic A(H1N1) after excluding persons with higher baseline antibody titers from analysis.
Pandemic and seasonal influenza A viruses had similar age-specific transmissibility in a cohort of initially uninfected households after adjustment for baseline immunity.
PMCID: PMC3206962  PMID: 21878814
17.  Viral shedding and clinical illness in naturally acquired influenza virus infections 
The Journal of infectious diseases  2010;201(10):1509-1516.
Volunteer challenge studies have provided detailed data on viral shedding from the respiratory tract before and through the course of experimental influenza virus infection. There are no comparable quantitative data on naturally-acquired infections.
In a community-based study in Hong Kong in 2008, we followed up initially well individuals to quantify trends in viral shedding based on culture and reverse transcription polymerase chain reaction (RT-PCR) through the course of illness associated with seasonal influenza A and B virus infection.
Trends in symptom scores more closely matched changes in molecular viral loads measured by RT-PCR for influenza A than influenza B. For influenza A virus infections, replicating viral loads measured by culture declined to undetectable levels earlier after illness onset than molecular viral loads. Most viral shedding occurred during the first 2–3 days after illness onset and we estimated that 1–8% of infectiousness occurs prior to illness onset. Only 14% of infections with detectable shedding by RT-PCR were asymptomatic, and viral shedding was low in these cases.
Our results suggest that ‘silent spreaders’ (i.e. individuals who are infectious while asymptomatic or pre-symptomatic) may be less important in the spread of influenza epidemics than previously thought.
PMCID: PMC3060408  PMID: 20377412
influenza; viral shedding; infectiousness
18.  Estimation of the serial interval of influenza 
Epidemiology (Cambridge, Mass.)  2009;20(3):344-347.
Estimates of the clinical-onset serial interval of human influenza infection (time between onset of symptoms in an index case and a secondary case) are used to inform public health policy and to construct mathematical models of influenza transmission. We estimate the serial interval of laboratory-confirmed influenza transmission in households.
Index cases were recruited after reporting to a primary healthcare center with symptoms. Members of their households were followed up with repeated home visits.
Assuming a Weibull model and accounting for selection bias inherent in our field study design, we used symptom-onset times from 14 pairs of infector/infectee to estimate a mean serial interval of 3.6 days (95% confidence interval = 2.9–4.3 days), with standard deviation 1.6 days.
The household serial interval of influenza may be longer than previously estimated. Studies of the complete serial interval, based on transmission in all community contexts, are a priority.
PMCID: PMC3057478  PMID: 19279492
19.  Effects of oseltamivir treatment on duration of clinical illness and viral shedding, and household transmission of influenza virus 
Large clinical trials have demonstrated the therapeutic efficacy of oseltamivir against influenza. Here we assessed its indirect effectiveness in reducing household secondary transmission in an incident cohort of influenza index cases and their household members.
We recruited index outpatients whose rapid tests for influenza were positive in 2007 and 2008. Household contacts were followed for 7–10 days during 3–4 home visits to monitor symptoms. Nose and throat swabs were collected and tested for influenza by reverse transcription polymerase chain reaction (RT-PCR) or viral culture.
We followed 384 index cases and their household contacts. Index cases who took oseltamivir within 24 hours of symptom onset halved the time to symptom alleviation (adjusted acceleration factor (AF) 0.56; 95% CI: 0.42, 0.76). Oseltamivir treatment was not associated with statistically significant reduction in the duration of viral shedding. Household contacts of index cases who had taken oseltamivir within 24 hours of onset had a non-statistically significant lower risk of developing laboratory-confirmed infection (adjusted odds ratio (OR) 0.54; 95% CI: 0.11, 2.57) and a marginally statistically significant lower risk of clinical illness (adjusted OR 0.52; 95% CI: 0.25, 1.08) compared to contacts of index cases who did not take oseltamivir.
Oseltamivir treatment is effective in reducing the duration of symptoms but evidence for household reduction in transmission of influenza virus was inconclusive.
PMCID: PMC2840043  PMID: 20121573
Influenza; oseltamivir; antiviral; public health
20.  Oseltamivir for treatment and prevention of pandemic influenza A/H1N1 virus infection in households, Milwaukee, 2009 
BMC Infectious Diseases  2010;10:211.
During an influenza pandemic, a substantial proportion of transmission is thought to occur in households. We used data on influenza progression in individuals and their contacts collected by the City of Milwaukee Health Department (MHD) to study the transmission of pandemic influenza A/H1N1 virus in 362 households in Milwaukee, WI, and the effects of oseltamivir treatment and chemoprophylaxis.
135 households had chronological information on symptoms and oseltamivir usage for all household members. The effect of oseltamivir treatment and other factors on the household secondary attack rate was estimated using univariate and multivariate logistic regression with households as the unit of analysis. The effect of oseltamivir treatment and other factors on the individual secondary attack rate was estimated using univariate and multivariate logistic regression with individual household contacts as the unit of analysis, and a generalized estimating equations approach was used to fit the model to allow for clustering within households.
Oseltamivir index treatment on onset day or the following day (early treatment) was associated with a 42% reduction (OR: 0.58, 95% CI: 0.19, 1.73) in the odds of one or more secondary infections in a household and a 50% reduction (OR: 0.5, 95% CI: 0.17, 1.46) in the odds of a secondary infection in individual contacts. The confidence bounds are wide due to a small sample of households with early oseltamivir index usage - in 29 such households, 5 had a secondary attack. Younger household contacts were at higher risk of infection (OR: 2.79, 95% CI: 1.50-5.20).
Early oseltamivir treatment may be beneficial in preventing H1N1pdm influenza transmission; this may have relevance to future control measures for influenza pandemics. Larger randomized trials are needed to confirm this finding statistically.
PMCID: PMC2919545  PMID: 20642862
21.  Entry screening to delay local transmission of 2009 pandemic influenza A (H1N1) 
After the WHO issued the global alert for 2009 pandemic influenza A (H1N1), many national health agencies began to screen travelers on entry in airports, ports and border crossings to try to delay local transmission.
We reviewed entry screening policies adopted by different nations and ascertained dates of official report of the first laboratory-confirmed imported H1N1 case and the first laboratory-confirmed untraceable or 'local' H1N1 case.
Implementation of entry screening policies was associated with on average additional 7-12 day delays in local transmission compared to nations that did not implement entry screening, with lower bounds of 95% confidence intervals consistent with no additional delays and upper bounds extending to 20-30 day additional delays.
Entry screening may lead to short-term delays in local transmission of a novel strain of influenza virus. The resources required for implementation should be balanced against the expected benefits of entry screening.
PMCID: PMC3152767  PMID: 20353566
22.  Preliminary Findings of a Randomized Trial of Non-Pharmaceutical Interventions to Prevent Influenza Transmission in Households 
PLoS ONE  2008;3(5):e2101.
There are sparse data on whether non-pharmaceutical interventions can reduce the spread of influenza. We implemented a study of the feasibility and efficacy of face masks and hand hygiene to reduce influenza transmission among Hong Kong household members.
Methodology/Principal Findings
We conducted a cluster randomized controlled trial of households (composed of at least 3 members) where an index subject presented with influenza-like-illness of <48 hours duration. After influenza was confirmed in an index case by the QuickVue Influenza A+B rapid test, the household of the index subject was randomized to 1) control or 2) surgical face masks or 3) hand hygiene. Households were visited within 36 hours, and 3, 6 and 9 days later. Nose and throat swabs were collected from index subjects and all household contacts at each home visit and tested by viral culture. The primary outcome measure was laboratory culture confirmed influenza in a household contact; the secondary outcome was clinically diagnosed influenza (by self-reported symptoms). We randomized 198 households and completed follow up home visits in 128; the index cases in 122 of those households had laboratory-confirmed influenza. There were 21 household contacts with laboratory confirmed influenza corresponding to a secondary attack ratio of 6%. Clinical secondary attack ratios varied from 5% to 18% depending on case definitions. The laboratory-based or clinical secondary attack ratios did not significantly differ across the intervention arms. Adherence to interventions was variable.
The secondary attack ratios were lower than anticipated, and lower than reported in other countries, perhaps due to differing patterns of susceptibility, lack of significant antigenic drift in circulating influenza virus strains recently, and/or issues related to the symptomatic recruitment design. Lessons learnt from this pilot have informed changes for the main study in 2008.
Trial Registration NCT00425893 HKCTR-365
PMCID: PMC2364646  PMID: 18461182

Results 1-22 (22)