Incidence of latent TB infection among hospital contacts in an intermediate-burden country.

BACKGROUND

This study aimed to investigate the incidence of latent tuberculosis infection (LTBI) and conversion rate among hospital inpatients contacts using an interferon-gamma release assay (IGRA)-based contact tracing strategy.

METHODS

We conducted a retrospective study at a 2,700-bed tertiary hospital in Seoul, South Korea. Data from January 2019 to December 2024 were reviewed. Contacts were recommended to undergo IGRA testing at the time of exposure (baseline) and again at ≥ 6 weeks later after exposure.

RESULTS

A total of 109 index cases required contact tracing, yielding 902 contacts, of whom 360 underwent IGRA testing between 1 and 6 months post-exposure (median, 48 days [interquartile range, 25-83]). At baseline, 79 (22%) tested IGRA-positive. Among 133 initially IGRA-negative individuals who underwent serial testing, 18 (14%) demonstrated IGRA conversion. Overall, 97 (27%) were diagnosed with LTBI.

CONCLUSIONS

Hospital-based contact investigation identified a substantial burden of latent TB infection among exposed individuals. IGRA conversion, rather than baseline positivity, may serve as a more reliable indicator of recent transmission in high or intermediate-burden settings, supporting the importance of serial testing in health care-associated TB exposure.