Wildfire-specific fine particulate matter and risk of hospital admissions in urban and rural counties

Background: The health impacts of wildfire smoke, including fine particles (PM_2.5), are not well understood and may differ from those of PM_2.5 from other sources due to differences in concentrations and chemical composition. Methods: First, for the entire Western United States (561 counties) for 2004-2009, we estimated daily PM_2.5 concentrations directly attributable to wildfires (wildfires-specific PM_2.5), using a global chemical transport model. Second, we defined smoke wave as ≥2 consecutive days with daily wildfire-specific PM_2.5 > 20 μg/m³, with sensitivity analysis considering 23, 28, and 37 μg/m³. Third, we estimated the risk of cardiovascular and respiratory hospital admissions associated with smoke waves for Medicare enrollees. We used a generalized linear mixed model to estimate the relative risk of hospital admissions on smoke wave days compared with matched comparison days without wildfire smoke. Results: We estimated that about 46 million people of all ages were exposed to at least one smoke wave during 2004 to 2009 in the Western United States. Of these, 5 million are Medicare enrollees (≥65 years). We found a 7.2% (95% confidence interval: 0.25%, 15%) increase in risk of respiratory admissions during smoke wave days with high wildfire-specific PM_2.5 (>37 μg/m³) compared with matched non smoke wave days. We did not observe an association between smoke wave days with wildfire-specific PM_2.5 ≤ 37 μg/m³ and respiratory or cardiovascular admissions. Respiratory effects of wildfire-specific PM_2.5 may be stronger than that of PM_2.5 from other sources. Conclusion: Short-term exposure to wildfire-specific PM_2.5 was associated with risk of respiratory diseases in the elderly population in the Western United States during severe smoke days. See video abstract at, http://links.lww.com/EDE/B137.