Risk Factors Associated With Time to Disease Onset Among Leprosy Contacts: A Cohort-Based Survival Analysis.

BACKGROUND

Leprosy is a chronic infectious disease affecting the skin and peripheral nerves, potentially causing deformities and disabilities. Transmission occurs mainly via aerosols and nasal secretions, with persistent endemicity in countries such as Brazil, India and Indonesia. Systematic monitoring of contacts is a key strategy for early detection and disease control.

OBJECTIVE

To investigate risk factors associated with time to disease onset among leprosy contacts and describe the temporal dynamics of disease development in a historical cohort.

METHODS

A retrospective cohort of 600 contacts of newly diagnosed leprosy cases (2002-2022) was followed for up to 5 years. Variables included age, Mitsuda test, anti-PGL-I IgM serology, qPCR in peripheral blood, BCG scar and type of contact. Disease-free survival was estimated with Kaplan-Meier curves and differences between groups were tested using the log-rank test. Variables with p < 0.20 were included in a multivariate Cox proportional hazards model, with stepwise removal until only variables with p < 0.05 remained.

RESULTS

During follow-up, 123 contacts (20.5%) developed leprosy, with a higher incidence in the first 24 months: 33.3% of cases occurred in the first year and 25.2% in the second year, followed by a relative stabilisation of new cases in subsequent years. Median survival time was 52 months. In multivariate analysis, positive qPCR (HR = 3.67; 95% CI = 2.42-5.55) and positive anti-PGL-I IgM (HR = 5.48; 95% CI = 3.79-7.92) were independently associated with earlier disease onset. Other factors, including age, Mitsuda test, BCG scar and type of contact, were not significant after adjustment.

CONCLUSIONS

Contacts with positive biomarkers face a higher risk of developing leprosy within 5 years. Understanding the temporal dynamics of disease onset supports targeted surveillance and timely intervention strategies, contributing to more effective leprosy control in endemic settings.