Symptom and chest radiographic screening for infectious tuberculosis prior to starting isoniazid preventive therapy: yield and proportion missed at screening.

OBJECTIVE

This analysis describes the prevalence of and risk factors for tuberculosis at screening prior to isoniazid preventive therapy (IPT); the additional yield of tuberculosis using chest radiography versus symptoms alone, and risk factors for tuberculosis missed by screening.

DESIGN

Cross-sectional analysis of a trial of community-wide IPT in South African gold mines.

METHODS

Participants were screened for tuberculosis prior to starting IPT using symptoms (cough >2 weeks, weight loss, night sweats) and chest radiography. Tuberculosis suspects had sputum collected for mycobacterial investigations. Those with a positive smear or culture with no speciation or culture identified as Mycobacterium tuberculosis were classified as having probable or definite tuberculosis, respectively. Among participants who were dispensed IPT, we defined a 'missed' case of active tuberculosis as one identified within 90 days of the enrolment screen.

RESULTS

Between July 2006 and December 2008, among 23,286 participants with complete data, the prevalence of undiagnosed tuberculosis [definite (284) and probable (31)] was high (315/23 286; 1.4%). The addition of chest radiography to symptom screening increased the number of definite tuberculosis cases detected by 2.5-fold (113 to 281 cases). Among 19,609 individuals correctly screened for tuberculosis who started IPT and had more than 90 days of follow-up, only 39 (0.2%) active tuberculosis cases were missed. Risk factors for tuberculosis missed by screening included increasing age [adjusted odds ratio (aOR) 1.66/10 year increase, 95% confidence interval (CI) 1.07-2.56], non-South African, in HIV care (aOR 4.80, 95% CI 1.63-14.1), lower weight (aOR 2.07/10 kg decrease, 95% CI 1.23-3.49) and alcohol use (aOR 2.52, 95% CI 1.31-4.86), which were similar to risk factors for tuberculosis detected by screening.

CONCLUSION

Tuberculosis screening prior to IPT detects a substantial burden of tuberculosis and misses very few cases. Chest radiography significantly increased the yield of tuberculosis cases detected.