Estimating the annual risk of infection with Mycobacterium tuberculosis among adolescents in Western Kenya in preparation for TB vaccine trials

Abstract Setting Siaya District, Western Kenya, with the highest TB notification rates in Kenya (400/100,000) Objective To determine the prevalence and annual risk of infection with M. tuberculosis (ARTI) among adolescents aged 12-18 years Design Adolescents aged 12-18 years were enrolled in an area under continuous health and demographic surveillance in 2008-2009. At enrolment, clinical and demographic data were collected and study participants screened for tuberculosis (TB) and for tuberculous infection using tuberculin skin tests (TST). Results Of 5004 adolescents enrolled, 4808 (96%) returned for TST readings. Of these 2327(48.4%) were female, 861 (17.9%) had no BCG scar, and 23 (0.5%) were HIV positive. The baseline prevalence of tuberculous infection was 32% (95% CI 29-35%) with a corresponding ARTI of 2.6% (95% CI 2.2-3.1%). Male gender (OR 1.3, 95%CI 1.2,1.5), having a BCG scar (OR 1.4,95%CI 1.3,1.7) and not being enrolled in school (OR 1.8, 95%CI 1.4,2.3) were independent predictors of a positive tuberculin skin test at baseline. Conclusion We found a high ARTI indicating very high TB transmission rates, suggesting that in this population prevention studies including TB vaccine trials would be both highly relevant and efficient.