Force of tuberculosis infection among adolescents in a high HIV and TB prevalence community: a cross-sectional observation study

Keren Middelkoop,Hua Liang,Robin Wood,Linda-Gail Bekker,Elaine Sebastian,Landon Myer,Lisa Dh Aquino

doi:10.1186/1471-2334-11-156

Abstract

BackgroundUnderstanding of the transmission dynamics of tuberculosis (TB) in high TB and HIV prevalent settings is required in order to develop effective intervention strategies for TB control. However, there are little data assessing incidence of TB infection in adolescents in these settings.MethodsWe performed a tuberculin skin test (TST) and HIV survey among secondary school learners in a high HIV and TB prevalence community. TST responses to purified protein derivative RT23 were read after 3 days. HIV-infection was assessed using Orasure® collection device and ELISA testing. The results of the HIV-uninfected participants were combined with those from previous surveys among primary school learners in the same community, and force of TB infection was calculated by age.ResultsThe age of 820 secondary school participants ranged from 13 to 22 years. 159 participants had participated in the primary school surveys. At a 10 mm cut-off, prevalence of TB infection among HIV-uninfected and first time participants, was 54% (n = 334/620). HIV prevalence was 5% (n = 40/816). HIV infection was not significantly associated with TST positivity (p = 0.07). In the combined survey dataset, TB prevalence was 45% (n = 645/1451), and was associated with increasing age and male gender. Force of infection increased with age, from 3% to 7.3% in adolescents ≥20 years of age.ConclusionsWe show a high force of infection among adolescents, positively associated with increasing age. We postulate this is due to increased social contact with infectious TB cases. Control of the TB epidemic in this setting will require reducing the force of infection.

Highlights

Understanding of the transmission dynamics of tuberculosis (TB) in high TB and HIV prevalent settings is required in order to develop effective intervention strategies for TB control
Of the 959 children enrolled in the secondary school, 839 were eligible for study participation (87%)
No study-related adverse events were noted in the three children assessed outside the window period and these participants were excluded from the analysis

Summary

Introduction

Understanding of the transmission dynamics of tuberculosis (TB) in high TB and HIV prevalent settings is required in order to develop effective intervention strategies for TB control. While repeated testing of with Mycobacterium tuberculosis in a specified period, can be calculated using changes in age-specific prevalence rates[10,11,12], and provides an estimate of recent infection incidence across a wider age range. This approach is a relatively new concept that has been utilized to estimate incidence in diseases in which true incidence is difficult or costly to measure, such as glaucoma[13] and more recently, HIV[12,14]. Data from this community suggest that TB transmission has remained relatively constant over the past decade, as evidenced by the stable TB notification rates among HIV-uninfected adults from 1997 to 2008[16], as well as the stable childhood TB over the same time period[2]

Methods

Results

Conclusion