Smoking, BCG and Employment and the Risk of Tuberculosis Infection in HIV-Infected Persons in South Africa

Tolu Oni,Tom H M Ottenhoff,Robert J Wilkinson,Kathryn Wood,Katalin A Wilkinson,Ronnett Seldon,Rene T Goliath,Nonzwakazi Bangani,Relebohile Tsekela,Hannah P Gideon,Jean Louis Herrmann

doi:10.1371/journal.pone.0047072

Abstract

BackgroundThe increased susceptibility to latent tuberculosis infection (LTBI) of HIV-1-infected persons represents a challenge in TB epidemic control. However few studies have evaluated LTBI predictors in a generalized HIV/TB epidemic setting.MethodsThe study recruited 335 HIV-infected participants from Khayelitsha, Cape Town between February 2008 and November 2010. Tuberculin skin tests and interferon-gamma release assays were performed on all participants and active TB excluded using a symptom screen, TB microscopy and culture.ResultsLTBI prevalence was 52.7% and 61.2% (TST and IGRA respectively). Being a recent TB contact (OR 2.07; 95% C.I. 1.15–3.69) was associated with TST positivity. Participants with a CD4>200 had a two-fold higher risk of IGRA positivity compared to those with CD4 counts <200 (OR 2.07; 95% C.I. 0.99–4.34). There was also a 19% increase in IGRA positivity risk for every additional year of schooling and a strong association between years of schooling and employment (p = 0.0004). A decreased risk of IGRA positivity was observed in persons with a BCG scar (OR 0.46; 95% C.I. 0.31–0.69) and in smokers (OR 0.47; 95% C.I. 0.23–0.96).ConclusionWe report the novel findings of a decreased risk of IGRA positivity in HIV-infected smokers possibly due to decreased interferon production, and in the persons with a BCG scar suggesting a protective role for BCG in this population. We also found an increased risk of TST positivity in employed persons, possibly due to ongoing transmission in public modes of transport.

Highlights

A high prevalence of latent tuberculosis infection (LTBI) globally means there remains a pool of M.tb. infection from which new cases will arise
Prevalence of TST and Interferon Gamma Release Assay (IGRA) Positivity We examined the LTBI prevalence using the TST and found a prevalence of 52.7% (95% C.I. 47.3%–58.3%)
Using the IGRA, the effect of immunosuppression was less marked with a higher prevalence of IGRA positivity compared to TST positivity (61.2% (95% C.I. 55.7%–66.4%)

Summary

Introduction

A high prevalence of latent tuberculosis infection (LTBI) globally means there remains a pool of M.tb. infection from which new cases will arise. A high prevalence of latent tuberculosis infection (LTBI) globally means there remains a pool of M.tb. HIV-1 (HIV)-infected persons are often overrepresented among TB cases, as the risk of re-infection and reactivation are greater. Detection of LTBI enables identification of HIV-infected persons who would benefit from preventive therapy. In high HIV/TB prevalence, low-income settings, screening the general population for LTBI poses significant operational and economic challenges. A greater understanding of risk factors for infection could enable more accurate identification of high-risk persons who might benefit from preventive therapy. A better comprehension of factors that increase the risk of TB infection could facilitate developing other interventions to attenuate this risk. The increased susceptibility to latent tuberculosis infection (LTBI) of HIV-1-infected persons represents a challenge in TB epidemic control. Few studies have evaluated LTBI predictors in a generalized HIV/TB epidemic setting

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