Incidence of Mycobacterium tuberculosis infection in an African city with endemic TB

BACKGROUND Transmission of Mycobacterium tuberculosis 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 M. tuberculosis infection. METHODS 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 M. tuberculosis infection was defined as IGRA conversion and further classified by sustained positive assays after conversion. RESULTS 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 M. tuberculosis infection was 3.3%. Older age, male sex, and drinking alcohol outside the home were associated with an increased risk of incident M. tuberculosis infection (rate ratio: 3.7). CONCLUSION 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 M. tuberculosis among men in the community could lead to novel case-finding interventions.