Associations of wildfire-derived particulate matter with hospitalization, emergency department visits and mortality: A systematic review and meta-analysis

Epidemiological studies on wildfire smoke exposure and its associated disease morbidities and mortalities are rapidly accumulating in recent years. However, the findings of the existing studies have not been quantitatively evaluated with a conclusion. We conducted a systematic review and meta-analysis for the studies focused on associations of wildfire-sourced particles (PM_2.5 and PM₁₀) with cardiorespiratory diseases and mortality. We reviewed all literatures related to wildfire particles (PM_2.5 and PM₁₀) and cardiorespiratory disease morbidities [hospital admission, emergency department (ED) visits] and mortality (all-cause and cause-specific) from January 1, 2000 to August 1, 2024. Meta-analyses were conducted to summarize Relative Risks (RRs) and 95% confidence intervals (CIs) across studies when at least three studies were available for a particular exposure-outcome. All articles were assessed for risk of bias using a standard tool (Grading of Recommendations Assessment, Development and Evaluation, GRADE) for quality assurance. Studies (N = 45) were increasingly published between the years of 2020–2024 and from North America (N = 21) and Australia (N = 11) where wildfires are common. In the meta-analysis of over 124 million patients, wildfire smoke was consistently associated with increased risk of all-cause mortality (RR: 1.02, 95% CI 1.01–1.03 for PM_2.5 per 10 μg/m³) and respiratory outcomes, including hospital admission (1.04, 95% CI 1.02–1.05 for wildfire PM_2.5 and 1.01, 95% CI 1.00–1.02 for wildfire PM₁₀) and ED visits (1.04, 95% CI 1.02–1.06 for wildfire PM_2.5). Associations between wildfire PM_2.5 and cardiovascular diseases were inconclusive (mortality: 1.02, 95% CI 1.01–1.03; hospital admission: 1.01, 95% CI 1.00–1.02; ED visit: 1.01, 95%CI: 0.98–1.04). Current studies provide evidence of an increased risk of hospitalization and ED visits for respiratory diseases and all-cause mortality due to wildfire PM_2.5 and PM₁₀ exposures worldwide. Future research is needed to explore health effects of wildfire exposure on cardiovascular diseases.