Incidence of tuberculous infection in a TB-endemic city

Abstract

<sec id="st1"><title>BACKGROUND</title>Current metrics for TB transmission include TB notifications, disease mortality, and prevalence surveys. These metrics are helpful to national TB programs to assess the burden of disease, but they do not directly measure incident infection in the community.</sec><sec id="st2"><title>METHODS</title>To estimate incidence of Mycobacterium tuberculosis infection in Kampala, Uganda, we performed a prospective cohort study between 2014 and 2017 which enrolled of 1,275 adult residents without signs of tuberculous infection (tuberculin skin test [TST] <5 mm and no signs of TB disease) and followed them for conversion of TST at 1 year.</sec><sec id="st3"><title>RESULTS</title>During follow-up, 194 participants converted the TST and 158 converted by one year. The incidence density of TST conversion was 13.2 conversions/100 person-year (95% CI 11.6–15.1), which corresponds to an annual cumulative incidence of tuberculous infection of 12.4% (95% CI 10.7–14.3). Cumulative incidence was greater among older participants and among men. Among participants who reported prior exposure to TB cases, the cumulative risk was highest among those reporting exposure during follow-up.</sec><sec id="st4"><title>CONCLUSIONS</title>The high annual incidence of infection suggests that residents of Kampala have adequate contact for infection with undetected, infectious cases of TB as they go about their daily lives.</sec>