Social Activity Patterns Drive High Rates of Latent Tuberculosis Infection among Adolescents in Urban Tanzania<br/>—Latent TB Infection in Adolescents, Tanzania

Abstract

SETTING: Dar es Salaam, Tanzania. OBJECTIVE: To determine the prevalence of latent tuberculosis (TB) infection (LTBI) among adolescents in a country with a high TB burden, and examine risks of LTBI according to their social activity patterns. METHODS: A cross-sectional study nested within a phase 2b randomised, placebo controlled, double blind study and consisted of 824 adolescents, 13 - 15 years old who had received Bacillus Calmette-Guerin (BCG) vaccine, were attending public secondary schools and had no evidence of active tuberculosis (TB). Anthropometric measurements were obtained, a questionnaire administered, and phlebotomy performed for a T spot interferon-γ release assay (IGRA) to detect LTBI. RESULTS: Among 824 subjects, 149 (18%) had a positive IGRA. After adjusting for the influence of household socioeconomic status, history of TB contact, living environment and nutritional status, LTBI risk was higher in subjects with than without regular informal encounters with traditional alcoholic beverage drinkers (AOR, 6.37 [1.84 - 22.00]). Other significant factors for LTBI risk included contact with TB patient at school (AOR, 3.34 [1.14 - 9.80]), and living close to a health facility, as was observed among those from houses within a 10 - 30-minute walking distance to the nearest health facility, who were less likely to be IGRA-positive than those who were living within a 10-minute walking distance (AOR, 0.30 [95%CI, 0.13 - 0.69]). CONCLUSION: This IGRA study revealed a high prevalence of LTBI among adolescents in Dar es Salaam, Tanzania with prior BCG immunization. Informal social encounters were identified as independent risk factors for LTBI, along with a history of contact with TB patients, living environment characteristics and household socioeconomic status. Efforts focusing on risk of MTB transmission in adolescents at informal social gatherings will improve interventions to reduce LTBI in this population and consequently the subsequent risk of developing active TB disease.