Background: WHO recommends treatment for latent tuberculosis infection (LTBI) in the homeless and people who use drugs (PWUD). The optimal test for LTBI screening is uncertain.
Methods: A cross-sectional study was conducted among the homeless and drug-rehabilitation clinic clients chronically using crack in Western Brazil. Participants were interviewed and offered HIV testing plus tuberculin skin testing (TST) and QuantiFeron®-Gold-in-Tube (QFT). We considered LTBI when either TST or QFT were positive. Factors associated with LTBI were adjusted in a multivariate model.
Results: Among 372 subjects with at least one valid test, 216 (58%) had LTBI. TST was not read in 18.4%; QFT was indeterminate in 2.5%. TST detected 27 (26%) extra LTBI cases among 75 QFT-negative individuals. PWUD had over three-fold odds for LTBI. TST was 4.5 times more likely to be positive in BCG-vaccinated individuals.
Conclusion: Given the high risk of progression to disease in this population, the high rates of loss to TST reading and the possibility of false-positive TST results from BCG vaccination, we endorse current CDC recommendations to use QFT for LTBI screening among the homeless and PWUD. However, because adding TST to a negative QFT increased LTBI detection considerably, TST should be considered in QFT-negative individuals.
Keywords: Crack cocaine; Interferon-gamma release assays; Latent tuberculosis infection; Tuberculin test.
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