Comparison of tuberculin test and interferon-gamma release assay for diagnosing latent tuberculosis in Community Health Workers, State of Rio Grande do Sul, Brazil, 2012

Objective: to compare the ability to detect latent Mycobacterium tuberculosis infection among community health workers using the tuberculin skin test (TST) and Interferon-gamma release assay (IGRA). Methods: this was a cross-sectional study conducted in Santa Cruz do Sul-RS, Brazil, applying TST and IGRA to 47 community health workers between March and June 2012. TST was considered positive when induration was >= 10mm. IGRA was considered positive when interferon-gama concentration was at least 0.35 IU/mL. Results: 12 community health workers presented positive TST and 6 had positive IGRA, the agreement between the tets was considered poor (k=0.063). Conclusion: despite the limited number of samples there is a high discrepancy between the tests, what emphasize the need for more studies to find a biological explanation for these differences and to examine the cost-benefit of using IGRA