Cross-sectional screening of healthcare workers at a regional chest clinic with an interferon gamma release assay: first report from Sri Lanka

Abstract

Sri Lanka is a moderate burden middle-income setting where healthcare workers (HCWs) are not routinely screened for TB infection, even in moderate to high transmission risk settings. This study evaluated the use of a commercial interferon gamma release assay (IGRA) in HCW screening in comparison to the tuberculin skin test (TST) in a regional chest clinic. HCWs (n = 39) serving at the study clinic, where over 500 TB patients are registered and treated every year, were screened for LTBI with both the TST and an IGRA. Factors associated with positive test results as well as agreement between the two tests were evaluated. 47.2% of HCWs screened were TST positive (10mmcut-off) and positivity was associated with working in poorly ventilated areas (P = 0.019, OR 5.133 (95% CI 1.23 – 21.35)), although not associated with working in the sputum laboratory or TB treatment room, age or gender. IGRA positivity was significantly lower, 15.7%(P = 0.003). Positivity was associated with male gender (P = 0.046) and a shorter duration of service at the chest clinic (P = 0.036), though it was not associated with work in risk areas. Agreement between tests (TST 10mm cut-off) was fair with a kappa of 0.30 (P = 0.013). Positive IGRA results were seen only in TST-positive subjects who had a TST reading of >15mm. Occupational and non-occupational factors associated with TST and IGRA positivity differed between tests. Short duration of service was associated with IGRA positivity. The IGRA showed no advantage over the TST as a test for LTBI in this setting.