Rise in Emergency Department Visits for Asthma During 2023 Canadian Wildfires

The 2023 wildfire season in Canada was unprecedented, with widespread fires including 29 mega-fires and the largest in Quebec’s history, spanning 1.2 million acres. These fires released massive amounts of smoke that enveloped large parts of Canada and the United States, leading to significant environmental and health impacts. In particular, recent research published in the Canadian Medical Association Journal highlights a notable increase in asthma-related emergency department (ED) visits across Ontario following intense smoke exposure in early June 2023.

The study analyzed data from 30 public health units, representing 95% of Ontario’s population, tracking ED visits from eight weeks before the wildfire peak through July 31, 2023. Researchers observed daily increases ranging from 11% to 24% in asthma-related ED visits during the initial heavy smoke episodes, with elevated rates persisting for up to six days after the first event. Interestingly, a second smoke episode later in July did not produce a similar increase, which may be attributed to factors such as pre-emptive medication use, caregivers administering maintenance medications to children, or behavioral adaptations like staying indoors and using air filtration.

Experts emphasize that wildfires, which are increasing in frequency and severity due to climate change, pose serious public health risks, especially to respiratory health. While acute respiratory issues are the most evident impacts, the broader health effects, including impacts on cognition, mental health, and diabetic control, are less well understood and warrant further research.

Dr. Hong Chen from Health Canada and associates notes that wildfire smoke’s primary health burden is on acute respiratory conditions, surpassing typical air pollution effects. Dr. Sarah Henderson from the BC Center for Disease Control advocates for a consistent national strategy to reduce indoor and outdoor exposure to wildfire smoke, given its widespread influence on air quality.

These findings underscore the urgent need for public health preparedness and adaptive measures to mitigate health risks associated with wildfires. The study titled "Impact of the 2023 wildfire smoke episodes in Ontario, Canada, on asthma and other health outcomes" can be accessed via the Canadian Medical Association Journal, DOI: 10.1503/cmaj.241506.

Source: https://medicalxpress.com/news/2025-05-ed-asthma-spiked-canadian-wildfires.html