District–level epidemiological trends of leptospirosis in Sri Lanka, 2006–2022

Sri Lanka has experienced recurrent leptospirosis outbreaks with significant morbidity and mortality, particularly among agricultural communities exposed to contaminated water and soil. Although the disease has been notifiable since 1991, comprehensive long-term analyses of its spatial and temporal patterns at the district level remain limited. This study aimed to describe the temporal trends and geographic distribution of leptospirosis in Sri Lanka using national surveillance data over a 17-year period. A retrospective descriptive study was conducted using national surveillance data on leptospirosis in Sri Lanka from 2006 to 2022, obtained from the Weekly Epidemiological Reports of the Epidemiology Unit. Population estimates from the Department of Census and Statistics were used to calculate incidence rates. Temporal trends and spatial distribution across the 25 districts were examined using R statistical software (version 4.3.1). Between 2006 and 2022, Sri Lanka reported substantial spatial and temporal heterogeneity in leptospirosis transmission, with 82,086 cases reported to the Epidemiology Unit during the study period. Wet Zone districts consistently reported the highest numbers of cases and remained hyper-endemic areas, with Ratnapura, Kalutara and Galle frequently reporting annual case counts exceeding 800–1,200 during peak transmission years. When expressed as incidence rates per 100,000 population, Kegalle and Matale frequently demonstrated higher incidence rates than more populous urban districts such as Colombo and Gampaha. Two major national surges were observed, with 7,295 cases reported in 2008 and a peak of 8,323 cases in 2020. While the southwestern region remained the core transmission area, a geographic shift occurred during the 2011 outbreak, when Kurunegala reported the highest number of cases among all districts. In contrast, Jaffna, Kilinochchi, Mannar, Mullaitivu, Vavuniya, Batticaloa, Ampara and Trincomalee consistently reported the lowest case numbers and incidence rates. Leptospirosis remains a persistent public health challenge in Sri Lanka, characterized by pronounced spatial heterogeneity and periodic national surges. The findings highlight the importance of district-level surveillance and population-adjusted analyses to identify high-risk areas and guide targeted interventions. Strengthening surveillance systems, expanding diagnostic capacity and implementing occupational and environmental risk-reduction strategies in high-burden districts are essential to improve control of leptospirosis in Sri Lanka.