Association of Short-Term Increases in Ambient Fine Particulate Matter with Hospitalization for Asthma or COPD during Wildfire Season and Other Time Periods

Background Short-term increases in air pollution are associated with poor asthma and chronic obstructive pulmonary disease (COPD) outcomes. Short-term elevations in fine particulate matter (PM2.5) due to wildfire smoke are becoming more common. Research Question This study evaluated whether short-term increases in PM2.5 and ozone in wildfire season and in winter inversion season were associated with a composite of emergency or inpatient hospitalization for asthma and for COPD. Study Design and Methods Case-crossover analyses evaluated 63,976 and 18,514 subjects hospitalized for primary discharge diagnoses of asthma and COPD, respectively, between January 1999 and March 2022. Subjects resided on Utah’s Wasatch Front where PM2.5 and ozone were measured by EPA-based monitors. Odds ratios (OR) were calculated using Poisson regression adjusted for weather variables. Results Asthma risk increased on the same day that PM2.5 increased during wildfire season (OR=1.057 per +10 μg/m3, CI: 1.019, 1.097, p=0.003) and winter inversions (OR=1.023 per +10 μg/m3, CI: 1.010, 1.037, p=0.0004). Risk decreased after 1 week, but during wildfire season risk rebounded at a 4-week lag (OR=1.098 per +10 μg/m3, CI: 1.033, 1.167). Asthma risk for adults during wildfire season was highest in the first 3 days after PM2.5 increases, but for children highest risk was delayed by 3-4 weeks. PM2.5 exposure was weakly associated with COPD hospitalization. Ozone exposure was not associated with elevated risks. Interpretation In a large urban population, short-term increases in PM2.5 during wildfire season were associated with asthma hospitalization and the effect sizes were greater than for PM2.5 during inversion season.