ED visits for asthma spiked during 2023 Canadian wildfires, study finds

New research in the Canadian Medical Association Journal found an increase in asthma-related emergency department (ED) visits across Ontario following heavy smoke in early June 2023.

Canada experienced the most destructive wildfire season to date in 2023, with difficult-to-control fires across the country, including 29 mega-fires. One fire in Quebec, the province’s largest-ever wildfire, extended 1.2 million acres. Smoke from fires blanketed Canada and the United States, causing substantial damage, loss, and displacement.

“The unprecedented wildfires of 2023 are a wake-up call that wildfires—a persistent feature of Canada’s landscape—are becoming more intense and prolonged in a changing climate, affecting millions of people,” writes Dr. Hong Chen, a scientist with Health Canada, ICES, and Public Health Ontario, with co-authors.

In early June, Ontario had some of the world’s worst air quality from wildfires in the neighboring province of Quebec.

To understand the impact on health, researchers conducted a study, analyzing ED visits throughout the period from eight weeks before a major wildfire event in early June until July 31, 2023, four weeks after a second fire that resulted in smoke.

The analysis included data from 30 public health units in Ontario, representing 95% of the population. They found daily increases of 11% to 24% in asthma-related emergency department visits over the first episode, continuing up to six days after it ended. However, the second period of heavy smoke did not result in an increase in asthma-related ED visits.

“Possible explanations [of the lack of effect during the second episode] include extended protective effects of preventive medications prescribed during the first episode, increased supply and use of medications (e.g., caregiver administration of maintenance medication to children), or improved behavioral adaptations to minimize exposure in keeping with air-quality advisories, such as staying indoors and using air filters.”

As wildfires are a major environmental risk factor around the world and are increasing in frequency and severity, the researchers note that more research is needed to better understand their impact on health and how to mitigate health effects.

“The biggest impact of wildfire smoke is on acute respiratory morbidity, where its effects are consistently greater than those of air pollution from other sources,” writes Dr. Sarah Henderson from the BC Center for Disease Control, in a related commentary.

“Less clear associations have been shown for a much wider range of acute health outcomes, including cognition, diabetic control, and mental health, among many others.”

Dr. Henderson highlights that wildfire smoke frequently affects air quality in the west and calls for Canada to develop a consistent approach to reducing indoor and outdoor exposures.