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

Abstract

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.

Keywords::

• Latent tuberculosis
• tuberculin skin test
• QuantiFERON
• homeless
• concordance

Acknowledgments

Our special thanks to the research committee and ethical committee of Pasteur Institute of Iran, which approved the study (no. 508), and the Centre for Communicable Disease Control in the Ministry of Health and Medical Education, which financially supported this project. The research team thank Dr Kayhan Azadmanesh (Pasteur Institute of Iran) for technical support and Dr Saber Esmaeili (Pasteur Institute of Iran) for logistical support, and Mr ZareSefat, Dr Jahangiri, Dr Rahimloo Aghdam, and Mr.Shahmiri (Welfare Organization, Tehran Municipality) and all the employees of the shelters who helped us in the sampling process. We are also grateful to Dr Ebrahim Ghaderi and Dr Ghobad Moradi of the Kurdistan University of Medical Sciences, who read and commented on earlier versions of the manuscript.

Declaration of interest: The authors declare that they have no competing financial interests.