Determinants of subclinical leprosy among household contacts in Indonesia: serological and socio-demographic factors

Background Leprosy remains a public health challenge in Indonesia, which ranks third globally after India and Brazil. Subclinical infection among household contacts contributes to ongoing transmission, as individuals infected with Mycobacterium leprae ( M. leprae ) without symptoms may serve as undetected reservoirs. This study investigated serological and sociodemographic determinants associated with subclinical M. leprae infection among household contacts of leprosy patients in Tangerang, Indonesia. Methods A cross-sectional study was conducted in 2020 among 320 household contacts of confirmed leprosy index cases recruited through purposive sampling. Anti-Phenolic Glycolipid-1 (PGL-1) IgM antibodies were detected using an in-house enzyme-linked immunosorbent assay (ELISA). Bivariate analysis using Chi-square and t -tests assessed preliminary associations, and multivariate logistic regression was applied to identify independent predictors of seropositivity, adjusting for potential confounders. Results Overall, 43.8% of household contacts were seropositive for anti-PGL-1 IgM antibodies. Multivariate analysis revealed that a history of Bacille Calmette-Guerin (BCG) vaccination was associated with significantly lower odds of seropositivity (adjusted OR = 0.514; 95% CI [0.291–0.907]; p = 0.018), while the presence of a visible BCG scar was associated with nearly twofold higher odds (adjusted OR = 1.953; 95% CI [1.117–3.415]; p = 0.024). No significant associations were found between sociodemographic factors such as age, sex, or contact duration, and seropositivity. Conclusion BCG vaccination status and visible BCG scars were key determinants of anti-PGL-1 seropositivity, suggesting complex interactions between vaccination, immune response, and exposure to M. leprae . The study highlights the protective role of BCG-induced immunity while emphasizing the need for standardized scar assessment and continuous surveillance of household contacts. Although limited by its cross-sectional and purposive design, the integration of immunological and epidemiological data represents a strength, providing evidence to support Indonesia’s Zero Leprosy 2030 control strategy.