Incidence of <i>Mycobacterium tuberculosis</i> infection in an African city with endemic TB

Abstract

<sec><title>BACKGROUND</title>Transmission of <i>Mycobacterium tuberculosis</i> often occurs in the community before diagnosis of TB is made. To measure the force of infection in an African city with endemic TB, we conducted a prospective cohort study of adults in Kampala, Uganda, to estimate the incidence of <i>M. tuberculosis</i> infection.</sec><sec><title>METHODS</title>Consenting volunteers with both a negative interferon-γ release assay (IGRA) and a negative tuberculin skin test were enrolled and followed for 18 months with quarterly IGRAs. New <i>M. tuberculosis</i> infection was defined as IGRA conversion and further classified by sustained positive assays after conversion.</sec><sec><title>RESULTS</title>In 998 eligible adults, the median age was 26 years, 61% were women, 62% had received bacille Calmette-Guérin vaccination, 12% were HIV-infected, and 25% drank alcohol. The overall annual risk of <i>M. tuberculosis</i> infection was 3.3%. Older age, male sex, and drinking alcohol outside the home were associated with an increased risk of incident <i>M. tuberculosis</i> infection (rate ratio: 3.7).</sec><sec><title>CONCLUSION</title>This prospective cohort study found a high rate of annual TB infection in an African city with endemic TB, especially among older men who drank alcohol outside the home. Screening for <i>M. tuberculosis</i> among men in the community could lead to novel case-finding interventions.</sec>.