Abstract

Leptospirosis is a climate-sensitive zoonosis whose transmission is associated with environmental and hydrological conditions, particularly in tropical regions. This ecological time-series study investigated the associations between leptospirosis incidence and climatic, hydrological, and structural variables in the Brazilian Amazon from 2005 to 2024 using annually aggregated data. Annual confirmed cases were obtained from national surveillance systems, while climatic and extreme-event data were derived from official meteorological and disaster databases. Associations were evaluated using generalized additive models with a negative binomial distribution. Leptospirosis incidence exhibited marked interannual variability without a significant temporal trend. Flooding events were significantly associated with increased incidence, whereas mean temperature and accumulated precipitation showed no independent association. Lagged precipitation emerged as a significant predictor, suggesting that environmental conditions associated with transmission may persist beyond the initial exposure period. Heavy rainfall events increased over time but were not associated with incidence. Sanitation coverage improved consistently but did not explain temporal variation in disease occurrence. These findings suggest that hydrological extremes and delayed precipitation patterns may serve as useful indicators of leptospirosis dynamics in the Brazilian Amazon. Incorporating these indicators into surveillance systems may improve the characterization of leptospirosis patterns in tropical regions.

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