Persistent and Emerging High-Risk Clusters of Leprosy Detection in Brazil: A Nationwide Spatiotemporal Analysis, 2001-2023.

BACKGROUND

Brazil accounts for a substantial share of the global leprosy burden, with persistent high-risk areas and marked spatial inequalities in case detection. Identifying spatiotemporal clusters of transmission is crucial for targeting surveillance and control efforts.

OBJECTIVE

To identify the spatial and temporal variation of high-risk clusters for leprosy detection in Brazil (2001-2023) and priority areas for intervention.

METHODS

This was a nationwide, population-based ecological study using Brazilian municipalities (n = 5570) as units of analysis. Frequencies, crude detection rates and age- and sex-adjusted detection rates of newly recorded leprosy cases were calculated, based on the national Notifiable Diseases Information System (SINAN). Kulldorff's spatial scan statistic (Poisson model) was applied to overlapping three-year periods to identify statistically significant high-risk clusters. Neighbouring categories and changes between consecutive triennia were compared to classify municipalities into clusters based on persistence, entry, or exit.

RESULTS

Over the study period, a total of 795,802 cases were reported (age- and sex-adjusted detection rate: 17.58/100,000 population; 95% CI: 17.54-17.62), with higher occurrence among males and residents of the Northeast region. Significantly high-risk clusters were concentrated in the North, Northeast, and Central-West regions; approximately 23% of municipalities were part of significant clusters in each triennium. The proportion of municipalities newly entering clusters increased from 10.7% (2003-2005 vs. 2001-2003) to 36.0% (2021-2023 vs. 2019-2021). In the most recent triennium (2021-2023), 16.9% of municipalities remained within significant clusters.

CONCLUSION

The persistence and (re)emergence of high-risk leprosy clusters in historically hyperendemic and socially vulnerable territories indicate sustained operational failures and demand programmatic prioritisation, with intensified surveillance, timely diagnosis and adequate treatment, particularly in the North, Northeast and Central-West regions of Brazil.