A Retrospective, Time-Stratified, Case-Crossover Study of the Effect of PM2.5 on Asthma Exacerbations in Rural Counties in Wisconsin

Air pollution is a pervasive environmental health hazard with the potential to worsen respiratory health outcomes, including asthma exacerbations. The impact of PM2.5 on asthma exacerbations among rural populations is not well understood. Our analysis used a retrospective, time-stratified, case-crossover study design to examine the relationship between PM2.5 and asthma exacerbations. We included asthma exacerbations that occurred January 1, 2019–June 30, 2022, among residents of seven rural counties in Wisconsin with a PM2.5 air monitor. We also used PM2.5 data collected by the Wisconsin Department of Natural Resources and weather data available from the National Oceanic and Atmospheric Administration (NOAA). Further, we used conditional logistic regression to assess the association between asthma exacerbations and lagged PM2.5 levels, adjusting for maximum daily temperature. We found PM2.5 levels (µg/m3) 2 days prior to exacerbation were significantly associated with asthma exacerbations (hazard ratio 1.184; 95% confidence interval (1.051, 1.344)). Our study demonstrated an increased hazard of asthma exacerbations with higher levels of PM2.5 in rural populations. These findings highlight the need for further research and efforts to mitigate the effects of air pollution in rural areas.