Quantifying the short-term mortality effects of wildfire smoke in Europe: a multicountry epidemiological study in 654 contiguous regions

Summary Background Fine particulate matter (PM2·5) from wildfire smoke could be more harmful to human health than that from other sources. Evidence of the short-term association between wildfire-related PM2·5 and mortality in Europe remains sparse, leading to uncertainties in the fire-related PM2·5 mortality burden. Methods In this retrospective, multicountry epidemiological study, we used the EARLY-ADAPT database to obtain daily mortality records in 654 contiguous subnational regions from 32 European countries, representing a population of 541 million individuals. We combined these data with daily estimates of fire-related and non-fire-related PM2·5 from the System for Integrated Modelling of Atmospheric Composition model during 2004–22. Regional and pooled associations between daily fire-related PM2·5 and all-cause and cause-specific mortality were quantified using quasi-Poisson regression. We compared deaths attributable to fire-related PM2·5 using relative risks (RRs) specific to fire-related PM2·5 versus total PM2·5. Findings Our study data included 95⸱3 million daily deaths for all-cause mortality, 19⸱5 million daily deaths for cardiovascular mortality, and 3⸱9 million daily deaths for respiratory mortality from Jan 1, 2004, until the latest available year in each country. Pooled cumulative (lags 0–7) RRs associated with a 1 μg per m3 increase in fire-related PM2·5 were 1⸱007 (95% CI 1⸱004–1⸱010) for all-cause mortality, 1⸱009 (1⸱006–1⸱013) for cardiovascular mortality, and 1⸱013 (1⸱008–1⸱019) for respiratory mortality. RRs were larger for fire-related PM2·5 than for non-fire-related PM2·5. Using RRs for total (fire-related and non-fire-related) PM2·5 underestimated the fire-related PM2·5 attributable mortality by 93%. Interpretation Associations with all-cause and cause-specific mortality were larger for fire-related compared with non-fire-related PM2·5. Assuming wildfire PM2·5 has the same effect as total PM2·5 substantially underestimates the mortality burden of wildfire smoke.