The epidemiological scenario of leptospirosis in Brazil from 2015 to 2024: An ecological study of socio-environmental and climatic determinants.

AbstractO_ST_ABSBackgroundC_ST_ABSLeptospirosis is a neglected tropical disease with substantial public health impact in Brazil, closely associated with socio-environmental vulnerabilities and climatic extremes. This study analyzed the epidemiological profile, spatiotemporal distribution, and climatic influences on leptospirosis incidence and lethality in Brazil from 2015 to 2024. MethodsAn ecological time-series study was conducted using secondary data from the Notifiable Diseases Information System (SINAN). Variables included geographic region, probable infection environment, occupational, and educational level (ISCED-2011). The spatiotemporal correlation between disease incidence and El Nino-Southern Oscillation (ENSO) anomalies was assessed using the Oceanic Nino Index (ONI) and Spearmans rank correlation coefficient. ResultsA total of 31,397 cases were notified, with an annual average of 3,140 cases. The South and North regions exhibited the highest incidence rates, while the Northeast and Southeast presented lethality rates above the national average (9.20%). A marked reduction in notifications occurred during the COVID-19 pandemic. Contaminations occurred predominantly in the domiciliary environment (64%). Rural workers (27.45%) and civil construction workers (18.63%) were the most affected occupational groups, with a higher incidence among illiterate and low-education populations. Climatic analysis revealed a positive spatial correlation between El Nino intensification and leptospirosis incidence in the South and Southeast, and a negative correlation in specific Northeastern states. ConclusionThe dynamics of leptospirosis in Brazil are complex and multifactorial, strongly influenced by macroclimatic variations and driven by deficits in basic sanitation and urbanization. Mitigating the disease burden requires sustained, region-specific public health strategies, targeted infrastructure improvements, and enhanced epidemiological surveillance to address underreporting. Author SummaryLeptospirosis is a life-threatening, neglected tropical disease that disproportionately affects vulnerable populations in Brazil. Despite its significant impact on public health, the way climatic events and socioeconomic factors interact to drive the disease remains complex and regionally distinct. In this comprehensive 10-year study (2015-2024), we analyzed over 31,000 cases across all Brazilian states. We discovered that the home environment is the primary site of infection, largely due to inadequate basic sanitation. The disease takes a severe toll on individuals with lower educational levels and those engaged in rural or civil construction work. Furthermore, we demonstrated that the El Nino climate phenomenon acts as a major spatiotemporal modulator for leptospirosis, triggering infection spikes in the flood-prone South and Southeast regions, while reducing cases during severe droughts in the Northeast. Our findings underscore that leptospirosis is not merely an infectious disease, but a direct symptom of socio-environmental vulnerability. These insights are crucial for public health policymakers to design localized, climate-informed early warning systems and to prioritize basic sanitation infrastructure where it is most urgently needed.