Causal effects of wildfire PM2.5 on hospital costs and length of stay in Brazil

To quantify the hospital burden of short-term wildfire-specific fine particulate matter (PM2.5), we linked 184.5 million patient-level hospitalizations across 449 Brazilian regions from 2000–2019 with daily wildfire-specific and non-wildfire PM2.5 estimates at 0.25° resolution. Using wind-driven variation in wildfire-specific PM2.5 within a space-time-stratified case-crossover framework, we estimated the effects of exposure on hospitalization costs and length of stay. Each 1 µg/m3 increase in wildfire-specific PM2.5 was associated with higher hospitalization costs for all-cause, respiratory, and cardiovascular diseases by 0.36%, 1.59%, and 0.25%, respectively, and longer stays by 0.63%, 1.72%, and 0.68%. Asthma and heart failure showed the largest cost increases, while asthma and pneumonia showed the largest increases in length of stay. Overall, wildfire-specific PM2.5 accounted for US$755.6 million in hospitalization costs and 30.8 million hospital days, with stronger relative effects among individuals aged 0–19 years and higher burdens in central-west Brazil. This study links 184.5 million hospitalizations in Brazil to wildfire-specific PM₂.₅, using wind-driven variation within a causal framework. It finds higher hospitalization costs and longer stays for all-cause, respiratory, and cardiovascular diseases, with stronger effects in children.