Wildfire smoke and dengue burden in Brazil: Evidence from a nationwide study

Wildfire fine particulate matter (PM_2.5) is an emerging health concern, yet its effects on mosquito-borne diseases, particularly dengue, remain unclear. Brazil faces one of the world's highest dengue burdens alongside frequent wildfires. We examined the association between short-term wildfire-specific PM_2.5 exposure and dengue-related hospitalizations across Brazil. We conducted a nationwide two-stage time-series analysis using daily dengue-related hospitalizations and daily wildfire-specific PM_2.5 concentrations across all Brazilian immediate-regions from 2008 to 2019. The wildfire-specific PM_2.5 estimates were derived from a chemical transport model and machine-learning calibration. Immediate region-specific associations between wildfire-specific PM_2.5 with dengue hospitalization risks were estimated using quasi-Poisson regression with distributed lag models and pooled using random-effects meta-analysis. Effect modification by socio-demographic factors, season, and forest cover was examined and attributable dengue hospitalizations were estimated. A 5 μg/m³ increase in wildfire-specific PM_2.5 (lag 0-7 days) was associated with a 10.5 % increase in dengue-related hospitalizations (Relative risk [RR]: 1.105 (95 % Confidence Interval [CI]: 1.060-1.152), stronger for dengue fever (RR: 1.094, 95 %CI: 1.049-1.141) than for Dengue Hemorrhagic Fever (DHF) (1.174, 0.754-1.831). Associations were consistent across sex, age groups, and regions, with higher risks in the elderly for DHF. Risks were greater during the dry season and in less densely populated areas. An estimated 28,994 dengue-related hospitalizations (95 % CI: 16,737-40,867) were attributable to wildfire-specific PM_2.5 exposure in Brazil, averaging 17.3 per 100,000 population annually. The Northeast region had the highest number of attributable dengue-related hospitalizations, while the Southeast region had higher population-level impact. No association was found with non-wildfire PM_2.5. Wildfire-specific PM_2.5 exposure increases dengue-related hospitalization risk in Brazil, underscoring the need to integrate wildfire smoke into dengue and vector surveillance and to target high-risk areas to reduce disease burden.