Smoking and HIV associated with subclinical tuberculosis: analysis of a population-based prevalence survey

BACKGROUND: Despite multiple tuberculosis (TB) prevalence surveys reporting a relatively high frequency of bacteriologically confirmed, active TB among individuals reporting no typical symptoms of disease, our understanding of this phenomenon is limited. OBJECTIVE: To quantify the epidemiological burden and estimate associations between individual-level variables and this "subclinical' presentation. METHODS: We performed a secondary analysis of TB prevalence survey data from the South African communities of the Zambia, South Africa Tuberculosis and AIDS Reduction trial. Generalized estimating equations were used to estimate the association between individual-level demographic, behavioral, socio-economic, and medical variables and the risk of bacteriologically positive TB among participants not reporting any symptoms consistent with active TB. RESULTS: The crude prevalence of TB was 2222.1 cases per 100000 population (95% CI 2053.4-2388.5); 44.7% (295/660) of all documented prevalent cases of TB were subclinical. Current tobacco smoking (OR 2.37, 95% CI 1.41-3.99) and HIV-positive status (OR 3.26, 95% CI 2.31-4.61) were significantly associated with subclinical TB. CONCLUSION: Individuals who smoke or have HIV may be at increased risk of active TB and not report typical symptoms consistent with disease. This suggests possible shortcomings of symptom-based case finding which may need to be addressed in similar settings.