Screening for latent tuberculosis infection in South Korean healthcare workers using a tuberculin skin test and whole blood interferon-gamma assay

Abstract

This study compared the results of a tuberculin skin test (TST) and a whole-blood interferon-gamma release assay (IGRA) to screen latent tuberculosis (TB) infection (LTBI) according to risk of TB exposure in South Korea. A cross-sectional comparison of 82 healthcare workers (HCWs) was performed from June 2009 to January 2010. Participants were grouped according to their risk for TB exposure: group 1, frequent and direct contact with active TB patients (n = 35); group 2, no known history of direct contact with active TB patients (n = 47). For the TST (10-mm induration cut-off), the positive response rate was 42.9% in group 1 and 34.0% in group 2 (p = 0.42). For the IGRA, the positive response rate was 40% in group 1 and 10.6% in group 2 (p = 0.002). Results obtained from the TST and the IGRA were not in significant agreement. The working duration of HCWs in TB-related departments was the only significant risk factor for LTBI (odds ratio 1.03; p = 0.031). Further, the IGRA can more accurately discriminate LTBI compared to the TST, based on the risk of TB exposure. These results suggest that the IGRA is diagnostically useful for LTBI in South Korean HCWs.