Differential Effects of Wildfire Smoke Fine Particulate Matter Exposure on Respiratory Disease Emergency Department Visits in the Western United States.

Abstract

<b>Rationale:</b> Wildfires significantly affect air quality in the western United States. Although prior research has linked wildfire smoke fine particulate matter (i.e., aerodynamic diameter ≦2.5 μm [PM_2.5]) to respiratory health outcomes, these studies typically have limited geographic and temporal coverage, lacking evidence from multiple states over extended periods. <b>Objectives:</b> To examine the differential acute effects of wildfire smoke and nonsmoke PM_2.5 exposure on respiratory disease emergency department visits in the western United States. <b>Methods:</b> We obtained data on more than 6 million emergency department visits for respiratory diseases, including asthma, chronic obstructive pulmonary disease, upper respiratory infections (URIs), and bronchitis, from five states in the western United States during 2007-2018. Daily exposure to wildfire smoke and nonsmoke PM_2.5 was estimated using a state-of-the-art model system. A time-stratified case cross-over design with conditional logistic regression models was used to assess the acute respiratory effects of smoke and nonsmoke PM_2.5 exposure. <b>Measurements and Main Results:</b> The odds ratios associated with a 1-μg/m³ increase in the 3-day average wildfire smoke PM_2.5 were 1.016 (95% confidence interval, 1.015-1.016) for asthma, 1.004 (1.003-1.005) for chronic obstructive pulmonary disease, 1.001 (1.000-1.011) for URIs, and 1.004 (1.004-1.004) for bronchitis. Wildfire smoke PM_2.5 had stronger estimated effects than nonsmoke PM_2.5, particularly for asthma (nonsmoke PM_2.5: odds ratio, 1.002; 95% confidence interval, 1.001-1.004). Stratified analyses showed greater vulnerability among women and adults. Sensitivity analyses confirmed robust associations across exposure windows, and concentration-response functions suggested no clear threshold for adverse effects. <b>Conclusions:</b> Wildfire smoke PM_2.5 was associated with increased risks of acute respiratory outcomes. Stronger effects were observed from smoke PM_2.5 than nonsmoke PM_2.5, particularly for asthma and URIs. These findings underscore the need for targeted public health interventions and further research into the unique toxicological properties of wildfire emissions.