Prevalent infectious tuberculosis in Harare, Zimbabwe: burden, risk factors and implications for control.

SETTING: Harare's high density suburbs. OBJECTIVES: To investigate the burden, duration and risk factors for prevalent tuberculosis (TB) and explore potential control strategies. METHODS: Randomly selected adults had TB culture, symptom screen and human immunodeficiency virus (HIV) serology. Prevalent TB was defined as undiagnosed or still culture-positive. Notification data and HIV prevalence in TB out-patients were used to estimate duration of infectiousness (prevalence/estimated incidence). RESULTS: Among 10 092 participants, 40 (0.40%, 95%CI 0.28-0.54) had prevalent smear-positive TB. HIV (adjusted odds ratio [aOR] 3.1, 95%CI 1.6-6.3, population attributable fraction [PAF] 33%), male sex (aOR 3.1, 95%CI 1.5-6.4, PAF 40%), and overcrowding (PAF 34%) were significant risk factors, with past TB treatment significant for HIV-negative participants only (PAF 7%). Recent household TB contact was not significant (PAF 10%). HIV prevalence was 21.1%; 76.9% of HIV-positive participants were previously untested. Duration of infectiousness was at least 18 weeks in HIV-positive and approximately 1 year in HIV-negative patients. CONCLUSIONS: Overcrowding, male sex and HIV infection were major risk factors for prevalent smear-positive TB. Reducing diagnostic delay may have greater potential to improve the control of prevalent TB than interventions targeted at household contacts, TB treatment outcomes, or TB-HIV interventions under current levels of awareness of HIV status.