Spatial and temporal dynamics of leptospirosis in South Brazil: A forecasting and nonlinear regression analysis

Although leptospirosis is endemic in most Brazilian regions, South Brazil shows the highest morbidity and mortality rates in the country. The present study aimed to analyze the spatial and temporal dynamics of leptospirosis cases in South Brazil to identify the temporal trends and high-risk areas for transmission and to propose a model to predict the disease incidence. An ecological study of leptospirosis cases in the 497 municipalities of the state of Rio Grande do Sul, Brazil, was conducted from 2007 to 2019. The spatial distribution of disease incidence in southern Rio Grande do Sul municipalities was evaluated, and a high incidence of the disease was identified using the hotspot density technique. The trend of leptospirosis over the study period was evaluated by time series analyses using a generalized additive model and a seasonal autoregressive integrated moving average model to predict its future incidence. The highest incidence was recorded in the Centro Oriental Rio Grandense and metropolitan of Porto Alegre mesoregions, which were also identified as clusters with a high incidence and high risk of contagion. The analysis of the incidence temporal series identified peaks in the years 2011, 2014, and 2019. The SARIMA model predicted a decline in incidence in the first half of 2020, followed by an increase in the second half. Thus, the developed model proved to be adequate for predicting leptospirosis incidence and can be used as a tool for epidemiological analyses and healthcare services.Temporal and spatial clustering of leptospirosis cases highlights the demand for intersectorial surveillance and community control policies, with a focus on reducing the disparity among municipalities in Brazil.Author summary: The southern region of Brazil has the highest morbidity and mortality from leptospirosis in the country. Here, we present an approach based on spatial and temporal modeling to help understand the incidence of leptospirosis in Rio Grande do Sul, an endemic state located in southern Brazil. Clusters of disease incidence and mortality were observed in Centro Oriental Rio Grandense and Metropolitan of Porto Alegre mesoregions, while no cases were recorded in 220 municipalities between 2007 and 2019. A model with satisfactory predictive ability was also developed. The high underreporting of cases may reflect the failure in the sensitivity of the state’s leptospirosis surveillance system. These results can assist public healthcare services in allocating appropriate efforts and resources to control the disease, specifically in these regions with a higher risk of leptospirosis, considering the growing need to clarify the dynamics of this neglected disease in Brazil.