SETTING: Dar es Salaam, Tanzania. OBJECTIVE: To determine the prevalence\nof latent tuberculosis (TB) infection (LTBI) among adolescents in a\ncountry with a high TB burden, and examine risks of LTBI according to their\nsocial activity patterns. METHODS: A cross-sectional study nested within a\nphase 2b randomised, placebo controlled, double blind study and consisted of\n824 adolescents, 13 - 15 years old who had received Bacillus Calmette-Gu�©rin\n(BCG) vaccine, were attending public secondary schools and had no evidence\nof active tuberculosis (TB). Anthropometric measurements were obtained, a\nquestionnaire administered, and phlebotomy performed for a T spot interferon-\n�³ release assay (IGRA) to detect LTBI. RESULTS: Among 824 subjects,\n149 (18%) had a positive IGRA. After adjusting for the influence of household\nsocioeconomic status, history of TB contact, living environment and nutritional\nstatus, LTBI risk was higher in subjects with than without regular informal\nencounters with traditional alcoholic beverage drinkers (AOR, 6.37\n[1.84 - 22.00]). Other significant factors for LTBI risk included contact with\nTB patient at school (AOR, 3.34 [1.14 - 9.80]), and living close to a health facility,\nas was observed among those from houses within a 10 - 30-minute\nwalking distance to the nearest health facility, who were less likely to be\nIGRA-positive than those who were living within a 10-minute walking dis-tance (AOR, 0.30 [95%CI, 0.13 - 0.69]). CONCLUSION: This IGRA study\nrevealed a high prevalence of LTBI among adolescents in Dar es Salaam, Tanzania\nwith prior BCG immunization. Informal social encounters were identified\nas independent risk factors for LTBI, along with a history of contact with\nTB patients, living environment characteristics and household socioeconomic\nstatus. Efforts focusing on risk of MTB transmission in adolescents at informal\nsocial gatherings will improve interventions to reduce LTBI in this population\nand consequently the subsequent risk of developing active TB disease.
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