Spatiotemporal trends in leptospirosis in the Philippines: a 10-year national surveillance analysis in a One Health and climate-related context

BackgroundLeptospirosis remains an important zoonotic disease in the Philippines, yet its long-term national and regional epidemiological patterns and implications for surveillance remain insufficiently characterized. This study aimed to (1) characterize temporal and spatial trends in reported human leptospirosis incidence in the Philippines from 2015 to 2024; (2) situate Philippine trends within the global epidemiological context; (3) interpret national and regional patterns through a One Health-informed perspective; and (4) examine their implications for surveillance and public health policy.MethodsA retrospective analysis of reported human leptospirosis cases and population data from 2015 to 2024 was conducted across Philippine regions. Incidence rates were calculated and temporal and regional variations were assessed using negative binomial regression with a log link and a maximum-likelihood-estimated dispersion parameter, using an offset for population. Candidate models (Poisson, negative binomial with fixed dispersion, negative binomial with estimated dispersion) were compared using deviance and Pearson dispersion ratios, the Akaike Information Criterion (AIC), and the Bayesian Information Criterion (BIC). The observed epidemiological patterns were interpreted in relation to established environmental and reservoir-related mechanisms reported in previous literature, without directly modeling animal, rainfall, or other hydrometeorological variables.ResultsA negative binomial regression model with an estimated dispersion parameter (k = 0.29) provided the best fit for Philippine leptospirosis data from 2015 to 2024 (AIC = 1891.82; BIC = 1976.48), outperforming both the Poisson model and a negative binomial model with fixed dispersion. Adjusting for region, national incidence demonstrated significant temporal variation (p < 0.001). Incidence in 2015, 2016, 2017, 2019, 2020 and 2021 was significantly lower than 2024 (the reference year), while 2018, 2022 and 2023 did not differ significantly from 2024. Regional variation was also significant (p < 0.001), with the Bangsamoro Autonomous Region in Muslim Mindanao (BARMM), the region with the lowest observed incidence, serving as the reference category. Fifteen of sixteen comparator regions showed significantly higher adjusted incidence than BARMM (adjusted IRR ranging from approximately 5.7 in Northern Mindanao to approximately 38.0 in Western Visayas, p < 0.001). Only SOCCSKSARGEN did not differ significantly from BARMM (aIRR = 1.45, p = 0.177).ConclusionReported human leptospirosis incidence in the Philippines exhibited significant temporal and spatial heterogeneity from 2015 to 2024, with a sustained higher national incidence beginning in 2022 and distinct regional risk profiles. These findings are consistent with the substantial burden of leptospirosis reported globally in tropical and subtropical settings and support a One Health-informed interpretation of the disease within the human–animal–environment interface. Environmental, hydrometeorological, and reservoir-related mechanisms may provide plausible contextual explanations based on previous evidence but were not directly evaluated in this study. The findings support regionally targeted surveillance and interventions, strengthened multisectoral coordination, and future integration of human, animal, environmental, and hydrometeorological data to improve leptospirosis risk assessment and early-warning capacity.