Extreme hydrological events shape temporal dynamics of schistosomiasis in the Amazon

Schistosomiasis is a neglected tropical disease whose transmission is strongly influenced by environmental and hydrological conditions. In tropical regions, increasing climate variability and the intensification of extreme events raise important questions regarding how long-term climatic conditions and hydrological disturbances shape disease dynamics. This study investigated the temporal association between schistosomiasis incidence, mean annual temperature, accumulated annual precipitation, and flooding occurrence over a 25-year time series (2000-2024) in an Amazonian municipality. Annual confirmed cases were obtained from the municipal surveillance system, while climatic data were extracted from national meteorological and disaster monitoring databases. Associations were evaluated using population-adjusted negative binomial regression models. We observed interannual variability in case numbers with epidemic peaks coinciding with years characterized by flooding events. Flood occurrence was significantly associated with increased incidence and appeared to exert its strongest influence within the same epidemiological year, whereas the climatic average represented by accumulated precipitation showed no significant association. Mean temperature was negatively associated with case numbers. Although the ecological design precludes causal inference, the findings highlight the epidemiological relevance of hydrological disturbances beyond climatic averages in shaping schistosomiasis dynamics. Incorporating flooding indicators into surveillance systems may enhance early identification of high-risk periods and guide targeted control strategies in tropical regions subject to increasing environmental instability.