Screening of EPTB patients for pulmonary involvement usually based on clinical symptoms, sputum examination and radiographic findings. This study describes the chest radiographic findings and sputum examinations of 74 EPTB patients. The main objective was to assess the value of CXRs and sputum examinations for identification of EPTB patients with pulmonary involvement who could be potentially infectious. Clinical predictors of culture positive sputum among EPTB patients were also evaluated.
In contrast to other studies (10), our results suggest that CXR is predictive of EPTB patients with pulmonary involvement. However, an important finding in this study was the high rate (23.5%) of normal CXR among patients with culture confirmed PTB.[10
] Interestingly, this rate was among non-HIV infected individuals with culture-positive TB. These results suggest that although CXR is predictive of positive sputum culture, it might not detect all EPTB patients with pulmonary involvement and highlight the importance of obtaining respiratory specimen cultures in the evaluation of persons with suspected TB, even those with normal CXRs. A recent observational cohort study[10
] has reported that of 601 respiratory culture-positive TB cases, 53 (9%) had normal CXRs. Twenty-two percent of them were HIV-infected patients. In another study[11
] conducted among patients with solely EPTB, the rate of normal CXR with positive-sputum culture was (19%). Although it appears that HIV infection may be a significant factor contributing to the incidence of pulmonary TB with a normal CXR, our study findings suggest that other factors may exist.
The reliability of CXRs in the diagnosis of TB is questionable.[12
] However, in the presence of cavities, the sensitivity and specificity of CXR becomes higher.[12
] The performance of CXR expressed as sensitivity and specificity in the diagnosis of culture positive TB cases is influenced by many factors. Abnormal, particularly apical radiographic abnormalities associated with TB are more expected in patients without underlying immunosuppression including HIV-infected patients and patients with renal disease.[10
] The interpretation of CXRs by radiologist is another important factor. The radiologist usually has little or no information about the patient and may have the tendency to under-read or over-read the chest radiographs. In one study using radiography found that 20% of the cases of active TB were reported as normal.[17
] Moreover, quality control in the interpretation of CXR is hardly practiced. In a large study[12
] conducted in Nairobi, Kenya involving 998 patients, the specificity of CXR was low (67%). The number of patients labeled as having TB using CXR with a negative culture that were placed treatment was high (22%) among all TB suspects.
In our study we found that 9 of 74 EPTB patients (12.1%) had sputum smears that were positive for acid-fast bacilli. This rate is relatively higher than previous report.[11
] Although it is assumed that smear-negative TB patients are not infectious, the transmission of TB from smear-negative, culture-positive patients has been documented in many studies.[8
] In one molecular epidemiological study among 1574 patients with pulmonary tuberculosis in San Francisco, patients with smear-negative culture-positive tuberculosis were responsible for 17% of tuberculosis transmission. In another similar study done by Hernandez-Garduo,[5
] patients with extra-pulmonary disease were included and represent 27% of the clustered cases in the Greater Vancouver regional district. Higher estimates of transmission were found when patients with EPTB alone were included (25-41%) than in patients with pulmonary disease suggesting the infective potential of patients with EPTB. In a recent molecular study done by Tostmann A[20
] including both pulmonary and extra-pulmonary TB cases, 13% of the secondary cases were attributable to transmission from patients with smear-negative TB.
Pulmonary tuberculosis patients including those having normal chest radiograph are usually symptomatic with cough/sputum being reported most commonly.[13
] In other series weight loss was found as a strong predictor of pulmonary and extra-pulmonary TB.[10
] In a recent study done by Wang, et al
, weight loss and fever were significantly found to be predictive of smear-positive TB patients[21
] In our study, although not statistically significant, night sweat, cough and weight loss were predictive clinical factors for positive sputum culture results in EPTB patients. Our findings suggest that sputum for M. tuberculosis
smear and culture should be obtained in those patients to enable prompt recognition of EPTB patients with pulmonary involvement.
In conclusion, in this studied population of patients, CXR results are predictive of positive sputum culture results. However, it is important to obtain respiratory specimen culture in the diagnosis of EPTB patients particularly in the presence of a relatively high rate of positive sputum culture and normal CXR findings. This may improve detection rates and lead to improved patients outcomes and reduced transmission of M. tuberculosis.