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

Abstract

Background: Adolescents are a prime target group for tuberculosis (TB) vaccine trials that include prevention of infection (POI). The BCG vaccine is given at birth and does not prevent TB infection. TB infection, a critical endpoint for POI vaccine trials would need to be documented to estimate sample sizes in target populations. Methods: Adolescents aged 12-18 years of age were enrolled in an area under continuous demographic surveillance. A tuberculin skin test (TST) survey was conducted as part of a study on TB prevalence and incidence. All adolescents got TSTs at enrolment and returned after 72 hours for reading. A TST of ≥10mm if HIV negative or ≥ 5mm if HIV positive, was considered positive. 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 conclude that the high TB transmission rates we found in this study, suggest that adolescents in this region may be an appropriate target group for TB vaccine trials including TB vaccine trials aiming to prevent infection.

Tuberculosis infection and disease in South African adolescents with perinatally acquired HIV on antiretroviral therapy: a cohort study

“…The prevalence of positive QFT at enrolment for the entire cohort was 32% with a cumulative prevalence of 46% after three years of follow-up at a median age of 15 years. This is similar to the prevalence reported in Western Kenya where at 14.4 years the prevalence of TB infection (using Tuberculin skin testing) was also 32%; however, only 0.5% adolescents were living with HIV in that study and 41% had unknown HIV status [14]. The prevalence in our study is similar to the 53% prevalence reported in Cape Town in 2011 in adolescents between 14 and 17 years [13].…”

“…Mtb infection can be measured using Interferon Gamma Release assays (IGRA), for example Quanti-FERON (QFT), a positive test denotes TB infection, however, further signs and symptoms and bacteriological evidence needs to be sought before the diagnosis of "TB disease" is made. Previous estimates of Mtb infection prevalence among adolescents in sub-Saharan Africa have indicated high annual risks among the general population but often lack data on HIV status [13,14]. In addition, a recent review that focused on bacteriologically confirmed pulmonary Tuberculosis (PTB) in adolescents and youth found no studies among those with HIV [15].…”