Comparison of an interferon-gamma release assay and the tuberculin skin test for diagnosis of latent tuberculosis in homeless people in Iran: a cross-sectional study.

BACKGROUND: The aim of this study was to evaluate of the concordance between the results of the tuberculin skin test (TST) and an interferon-γ release assay (QuantiFERON test, QFT-GIT) for diagnosis of latent tuberculosis infection (LTBI) in homeless people in Tehran city, Iran.

METHODS: This cross-sectional study was conducted from June to August 2012. Homeless people were eligible to participate in the study if they were 18-60 years old.

RESULTS: Among 569 homeless people, 46.22% (95% confidence interval (CI) = 42.16-50.33%) and 20.39% (95% CI = 17.28-23.9%) were QFT-GIT and TST positive, respectively. Among these participants, the prevalence of LTBI with positivity of at least one of the tests was 52.2%. The overall agreement between QFT-GIT and TST was 62.21% (kappa = 0.21, 95% CI = 0.13-0.29, p < 0.001). Factors associated with positive results in QFT-GIT and TST were older age, being male, having a longer history of homelessness and having a history of incarceration in the last 10 years.

CONCLUSIONS: A high prevalence of LTBI was seen among homeless people in this study. There was a poor concordance between QFT-GIT and TST among this group. To better assess the utility of QFT-GIT in detection of LTBI further studies with a low prevalence of LTBI in this group are recommended.