Short-term increases in fine particulate matter (PM2.5) resulting from wildfire smoke are becoming a greater global problem and have been associated with poor asthma and COPD outcomes, wrote Benjamin D. Horne, PhD, of the Intermountain Medical Center Heart Institute, Salt Lake City, Utah, and colleagues. However, the effect of short-term increases in PM2.5 on hospitalizations for asthma and COPD has not been well studied, they noted.
“Our primary reason for studying the association of air pollution in the summer/fall wildfire season separately from the winter is that the drought conditions in the western United States from 2012-2022 resulted in more wildfires and increasingly large wildfires across the west,” Dr. Horne said in an interview. “In part, this provided a chance to measure an increase of fine particulate matter (PM2.5) air pollution from wildfires and also to track what happened to their health when people were exposed to the PM2.5 from wildfire,” he said.
During 2020-2022, the PM2.5 produced during the wildfire season exceeded the PM2.5 levels measured in the winter for the first time, Dr. Horne said. In the part of Utah where the study was conducted, PM2.5 increases in winter because of a combination of concentrated PM2.5 from cars and industry and a weather phenomenon known as a temperature inversion, he said.
A temperature inversion occurs when mountain topography traps pollutants near the ground where the people are, but only during times of cold and snowy weather, Dr. Horne said.
“Past studies in the region were conducted with the assumption that the winter inversion was the primary source of pollution-related health risks, and public and healthcare guidance for health was based on avoiding winter air pollution,” Dr. Horne noted. However, “it may be that the smoke from wildfires requires people to also anticipate how to avoid exposure to PM2.5 during the summer,” he said.
In a study published in CHEST Pulmonary, the researchers reviewed data from 63,976 patients hospitalized with asthma and 18,514 hospitalized with COPD between January 1999 and March 2022 who lived in an area of Utah in which PM2.5 and ozone are measured by the Environmental Protection Agency. The average age of the asthma patients was 22.6 years; 51.0% were women, 16.0% had hypertension, and 10.1% had a history of smoking. The average age of the COPD patients was 63.5 years, 50.3% were women, 69.1% had hypertension, and 42.3% had a history of smoking.
In a regression analysis, the risk for asthma was significantly associated with days of increased PM2.5 during wildfire season and similar to the winter inversion (when cold air traps air pollutants), with odds ratios (ORs) of 1.057 and 1.023 for every 10 µg per m3 of particulate matter, respectively.
Although the risk for asthma hospitalization decreased after a week, a rebound occurred during wildfire season after a 4-week lag, with an OR of 1.098 for every 10 µg per m3 of particulate matter, the researchers wrote. A review of all months showed a significant association between a concurrent day increase in PM2.5 and asthma hospitalization (OR, 1.020 per every 10 µg per m3 of particulate matter, P = .0006).
By contrast, PM2.5 increases had only a weak association with hospitalizations for COPD during either wildfire season or winter inversion season, and ozone was not associated with increased risks for patients with asthma or COPD.
The findings were limited by several factors including the observational design, potential for confounding, and relatively homogeneous study population, the researchers noted.
However, “these findings suggest that people should be aware of the risks from wildfire-generated PM2.5 during the summer and fall, including following best practices for people with asthma such as anticipating symptoms in warm months, carrying medications during summer activities, and expecting to stay indoors to avoid smoke exposure when wildfires have polluted the outdoor air,” Dr. Horne told this news organization.
In the current study, Dr. Horne and colleagues expected to see increases in the risk for asthma and COPD during summer wildfire season. “What was surprising was that the size of the risk of needing care of asthma appeared to occur just as rapidly after the PM2.5 became elevated during wildfire events as it did in the winter,” said Dr. Horne. “Further, the risk in the summer appeared to be greater than during the winter. Increases in hospitalization for asthma occurred on the same day and throughout the first week after a rise in air pollution in summer and early fall, and especially in children that risk remained increased for up to a month after the rise in air pollution,” he said.
Clinicians should be aware of environmental sources of respiratory declines caused by wildfire smoke that may prompt patients to seek care during wildfire events, said Horne. Finally, the general population should recognize the smell of smoke during warm months as an alert that leads to greater caution about spending time outdoors during wildfire events, he said. “Short-term PM2.5 elevations may affect respiratory health and have other effects such as on heart health,” Dr. Horne said. “In general, people should avoid outdoor exercise when air pollution is elevated, since the amount of air that is breathed in during exercise is substantially increased,” he added.
“Further research is needed regarding the mechanisms of effect from PM2.5 on health risk, including effects on respiratory and cardiovascular health,” said Dr. Horne. “This includes evaluating what biomarkers in the blood are changed by air pollution such as inflammatory factors, determining whether some medications may block or reduce the adverse effects of air pollution, and examining whether masks or indoor air purifiers have a meaningful benefit in protecting health during short-term air pollution elevations,” he said.