Seven-year surveillance of latent tuberculosis infection using interferon-gamma release assay among health workers at a large tertiary hospital in Thailand

BACKGROUND: Despite ongoing TB control efforts, health workers (HWs) in Thailand remain at risk for latent tuberculosis infection (LTBI), yet the burden of LTBI in Thai HWs is insufficiently characterized. This study aimed to determine LTBI proportions across preplacement, post-exposure, and annual screening approaches, and to identify factors associated with LTBI among HWs. METHODS: This retrospective analysis (2016-2022) utilized secondary data from an LTBI surveillance program at a large Thai tertiary hospital. HWs underwent LTBI screening with interferon-gamma release assays (IGRAs) through three surveillance approaches: preplacement, post-exposure, and annual screening in high-risk units (2021-2022). LTBI was defined as IGRA-positive in the absence of active TB. Demographic and exposure characteristics were recorded; associations were analyzed using chi-square and Mann-Whitney U tests. An exploratory restricted analysis using multivariable logistic regression was also performed to assess between-cohort patterns. RESULTS: Between 2016 and 2020, LTBI was detected in 198 of 1,823 HWs (10.9%; 95% CI: 9.5-12.4). Preplacement screening identified LTBI in 96 of 1,230 HWs (7.8%; 95% CI: 6.5-9.5), while post-exposure surveillance detected LTBI in 102 of 706 HWs (14.4%; 95% CI: 12.1-17.2). Annual surveillance (2021-2022) yielded 47 cases among 626 HWs (7.5%; 95% CI: 5.7-9.8). Among HWs diagnosed with LTBI in the preplacement and post-exposure cohorts, 40.9% of LTBI cases initiated TB preventive treatment. In post-exposure surveillance, older age and higher exposure-priority categories were associated with LTBI, although estimates for priority categories were imprecise because of sparse data. CONCLUSIONS: LTBI remains an important occupational health concern among HWs, with the highest detection proportion observed during post-exposure surveillance. These findings highlight the ongoing need for targeted, risk-based monitoring and efforts to enhance TB preventive treatment uptake in healthcare settings.