Age-stratified prevalence of latent tuberculosis infection in Ulaanbaatar, Mongolia: a facility-based cross-sectional study.

OBJECTIVES

Mongolia has a high tuberculosis (TB) burden. This study aimed to assess the age-specific latent TB infection (LTBI) prevalence in a healthy population in Mongolia by using interferon-gamma release assays.

METHODS

This facility-based cross-sectional study was conducted from June 2024 to March 2025 in Ulaanbaatar. Eligible participants were asymptomatic, aged ≥10 years, had no previous TB treatment, and had no known contact with TB. LTBI was detected using the QuantiFERON-TB Gold Plus (QFT-Plus) assay. Sociodemographic data were collected using standardized questionnaires.

RESULTS

The overall QFT-Plus positivity rate in 766 eligible participants (mean age: 38.2 years; 47.1% female) was 33.4%. Age-specific positivity increased from 7.9% (participants aged 10-19 years) to 46.1% (participants aged ≥60 years, P < 0.0001). Sex was not associated with positivity (P = 0.652), although the rate was slightly higher in women aged 40-59 years than in men. Multivariable analysis confirmed that age was a significant predictor of QFT-Plus positivity, reflecting TB prevalence.

CONCLUSION

Ulaanbaatar's LTBI prevalence remains high, especially among older adults, suggesting a shift from recent transmission to remote infection reactivation. Although QFT-Plus positivity in young individuals remains high, our findings support the prioritization of targeted preventive strategies for older populations.