Emergency Department Visits for Asthma Increased During 2023 Wildfires

May 06, 2025

MONDAY, May 5, 2025 (HealthDay News) — Increases in asthma-related emergency department visits were seen in Ontario in association with the 2023 wildfires, according to a study published online May 5 in CMAJ, the journal of the Canadian Medical Association.

Hong Chen, Ph.D., from Health Canada in Ottawa, Ontario, and colleagues conducted a quasi-experimental study by leveraging the timing of two consecutive wildfire smoke episodes in June 2023. On two occasions, in early June and in late June, heavy wildfire smoke blanketed much of Ontario, causing severely degraded air quality. Health data were collected on emergency department visits for four outcomes: asthma-related causes, other respiratory causes, ischemic heart disease, and noncardiorespiratory causes.

The researchers observed a substantial increase in daily asthma-related visits across Ontario after the initial heavy wildfire smoke in early June 2023, peaking at a 23.6 percent increase at a one-day lag and lasting up to a lag of five days following the start of the smoke episode. The later episode of heavy smoke caused higher exposures, but had a lesser effect on asthma-related visits. No effect was seen on other outcomes in either episode. In a post-hoc analysis, asthma-related visits were briefly elevated after the wildfire among children (increase of 40 percent), but among adults, a more sustained effect was seen (48 percent higher, lasting one week).

“The effects of wildfire smoke pollution are consistent with air pollution from other sources, but wildfire smoke emissions cannot be regulated at their source,” Sarah B. Henderson, Ph.D., from the British Columbia Centre for Disease Control in Vancouver, Canada, writes in an accompanying editorial. “Relying on people to protect themselves is not enough, and top–down strategies — such as building measures to ensure quality of indoor air and legislation to protect outdoor workers — are also needed to protect human health as the climate continues to change.”

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