ADVANCEMENT OF THE SCIENCE
Open Access
A Retrospective, Time-Stratified, Case-Crossover Study of the Effect of PM 2.5 on Asthma Exacerbations in Rural Counties in Wisconsin
Our study’s aim was to investigate the association between PM 2.5 and asthma exac- erbations in rural areas of Wisconsin because most previous studies have focused on urban centers. Assessing time-varying pollutant exposures on asthma exacerbations can be challenging, however, particularly when working with administrative data sets that only include cases. To overcome this chal- lenge, we employed the case-crossover study design, which uses cases and self-matched referent periods to e ectively control for con- founding characteristics (Maclure, 1991). In recent years through public health sur- veillance, we have observed that some rural counties in Wisconsin have experienced increasing rates of asthma-related emergency department visits and hospitalizations, and we hypothesized that poor air quality could be a contributing factor. Given the important role of agriculture in Wisconsin’s rural economy, agricultural practices such as prescribed burn- ing, soil tilling, livestock operations emis- sions, and farm equipment use could gener- ate substantial amounts of PM 2.5 (Domingo et al., 2021; U.S. Environmental Protection Agency, 2024). Additionally, wildfires occur- ring in other U.S. states and Canada can lead to high levels of particulate matter that adversely a ect the air quality in Wisconsin. Our study examined the relationship between PM 2.5 and asthma exacerbations in seven rural counties in Wisconsin. Although one study that spanned both rural and urban popula- tions examined the impact of PM 2.5 on asthma exacerbations (Bozigar et al., 2021), our study is the first to specifically focus on rural popu- lations, contributing to the understanding of the impact of air pollution on asthma exacer- bations in rural areas. Megan Elderbrook, MPH, CHES Wisconsin Asthma Program, Wisconsin Department of Health Services Ron Gangnon, PhD Department of Population Health Sciences and Department of Biostatistics and Medical Informatics, School of Medicine and Public Health, University of Wisconsin-Madison Carrie Tomasallo, MPH, PhD Wisconsin Asthma Program, Wisconsin Department of Health Services
Abstract Air pollution is a pervasive environmental health hazard with the potential to worsen respiratory health outcomes, including asthma exacerbations. The impact of PM 2.5 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 be- tween PM 2.5 and asthma exacerbations. We included asthma exacerbations that occurred January 1, 2019–June 30, 2022, among residents of seven ru- ral counties in Wisconsin with a PM 2.5 air monitor. We also used PM 2.5 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 asso- ciation between asthma exacerbations and lagged PM 2.5 levels, adjusting for maximum daily temperature. We found PM 2.5 levels (µg/m 3 ) 2 days prior to exacerbation were significantly associated with asthma exacerbations (haz- ard ratio 1.184; 95% confidence interval [1.051, 1.344]). Our study dem- onstrated an increased hazard of asthma exacerbations with higher levels of PM 2.5 in rural populations. These findings highlight the need for further research and eorts to mitigate the eects of air pollution in rural areas. Keywords: asthma, respiratory health, air pollution, PM 2.5 , rural health
Introduction Asthma is a prevalent chronic lung disease that a ects approximately 1 in 10 children (Centers for Disease Control and Prevention [CDC], 2023a) and 1 in 7 adults in Wiscon- sin (CDC, 2023b). Asthma symptoms can be triggered by tobacco smoke, dust mites, pests, mold, pets, and outdoor air pollution (CDC, 2024). Outdoor air pollution varies by geography (Strosnider et al., 2017) and
is influenced by seasonal weather patterns (Winquist et al., 2014). PM 2.5 is one of the most ubiquitous pollutants and has been shown to exacerbate asthma symptoms. Mul- tiple epidemiological studies have demon- strated that PM 2.5 levels are positively corre- lated with asthma symptoms (Berhane et al., 2016), emergency department visits (Romieu et al., 1996), hospitalizations (Zheng et al., 2015), and mortality (Atkinson et al., 2014).
8
Volume 87 • Number 6
Powered by FlippingBook