Climate-sensitive infectious diseases in the context of climate change: Lessons from Brazil's floods, with leptospirosis as an example.

Abstract

Climate variability and extreme weather events may impact climate-sensitive infectious diseases, one example being leptospirosis. This study provided an updated descriptive and exploratory analysis of leptospirosis in Brazil, focusing not only on temporal and regional patterns, but also on the 2024 floods in Rio Grande do Sul, which lent themselves to interpretation of climate-related health effects. Nationwide surveillance data on reported leptospirosis cases, deaths, and case-fatality rates were analyzed across Brazil's five geographic regions from 2014 to 2025, together with mean annual regional precipitation data. Exploratory correlation analyses were conducted using data from 2014 to 2024. While data from 2025 were included descriptively, the epidemiological dataset was incomplete, rendering corresponding precipitation data unavailable, and these data were excluded from correlation analyses. Additional analyses dealt with the epidemiological situation during the 2024 floods in Rio Grande do Sul. Between 2014 and 2024, Brazil reported 36,261 leptospirosis cases and 3170 deaths. Nationwide, cases increased from 3428 in 2023 to 4142 in 2024, and deaths from 290 to 362. The southern region showed the largest increase, from 1238 to 1988. During the 2024 floods in Rio Grande do Sul, 242 confirmed cases, 17 deaths, and 3270 suspected cases were reported. Even though exploratory analyses identified positive correlations between annual precipitation and leptospirosis cases and deaths in the South and nationwide, their associations were heterogeneous. As they illustrate the complexity of assessing climate-related health effects in cases of leptospirosis, these findings should not be interpreted as evidence of causality. Integrated epidemiological, climatic, environmental, and socioeconomic surveillance is essential to the development of climate-informed preparedness and of timely responses to climate-sensitive infectious diseases.