Estimating the burden of leptospirosis in the Caribbean: Insights from environmental and sociodemographic factors

IntroductionPrevious studies up to early 2000s found that leptospirosis incidence in humans was high across the Caribbean region (CR), yet up-to-date and reliable surveillance data are scarce. Limited research capacity in the region has further contributed to less robust characterisation of transmission drivers, perpetuating a cycle of neglect. To address these gaps and support evidence-based public health responses, this study aims to update incidence estimates in the CR by integrating data from multiple data sources, including peer-reviewed publications, surveillance reports and environmental and sociodemographic datasets. Methodology/Principal FindingsWe used mixed-effects hierarchical Poisson models at the country/territory-year level, incorporating covariates i.e., precipitation, temperature, gross domestic product, biodiversity loss, human footprint, water flow accumulation index, populations exposed to forested areas and frequency of extreme weather events to estimate annual case numbers by country/territory. Temporal patterns in case fatality rate (CFR) were modelled using locally estimated scatterplot smoothing regressions. Between 2001 and 2023, we estimated 32,311 (95% CI 28,646-36,832) cases in the region. Annual incidence (cases/100,000 population) showed a decrease trend, with small- to medium-sized population islands exhibiting the highest predicted incidence (Guadeloupe 22.7 (95%CI 20.5-25.0) and Saint Vincent and the Grenadines 22.3 (95%CI 17.6-27.9)). Estimated CFR increased over the study period, from 8.8% (95%CI 4.1-13.4) (2001) to 12.2% (.2.2-22.2) (2022). Conclusions/SignificanceLeptospirosis remains an important and often overlooked public health concern in the CR, where small island developing states bear a disproportionate burden of the disease. These findings underscore the urgent need for strengthening and integrating the surveillance systems and laboratory capacity in the region, particularly in small states, to provide accurate data to support cost-effective public health interventions. Authors summaryLeptospirosis is a bacterial infection that affects both animals and humans and is common across the Caribbean. Yet, many countries and territories in the region lack reliable and up-to-date information on disease incidence and mortality. This is partly due to limited laboratory capacity, inconsistent case reporting, and competing health priorities. As a result, the true burden of leptospirosis remains unclear, especially for resource-limited small island nations, which are vulnerable to potential impacts of climate change and extreme weather events on leptospirosis transmission. In this study, we combined information from peer-reviewed publications, national surveillance reports, and environmental and sociodemographic datasets to estimate annual incidence and mortality across the Caribbean. Using statistical modelling, we estimated over 32,000 cases between 2001 and 2023, with small- and medium-sized islands showing the highest incidence (cases/100,000 population). We also estimated a slight increase in case-fatality rate over time. Our findings highlight that small island developing states carry a disproportionate burden of this disease. Improving local surveillance systems and strengthening regional level collaboration are essential to help countries better identify risk, prepare for outbreaks, and reduce illness and deaths.