Asthma-related emergency department (ED) visits spiked in Ontario following the heavy smoke that came with Canada’s most destructive wildfire season, according to new research published in the Canadian Medical Association Journal on Monday.
“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 Hong Chen, a scientist with Health Canada, ICES, and Public Health Ontario, with coauthors.
Thick smoke from severe wildfires blanketed Canada but also the United States in 2023, destroying forests and homes and worsening air quality.
Researchers focused on the impacts of smoke from two wildfires on residents of Ontario, analyzing ED visits from 30 public health units in the summer of 2023. The study was conducted over a period that began around eight weeks before the first wildfire and lasted four weeks after the second one.
In early June 2023, when heavy wildfire smoke from neighbouring Quebec reached Ontario, researchers found that daily increase in asthma syndromes and ED visits rose by between 12 per cent and 23.2 per cent above the norm, depending on the age group and number of days passed since the start of the smoke.
However, researchers say they did not observe similar increases during the second episode of heavy smoke in late June.
“Although the exact reason is unknown, possible explanations include extended protective effects of preventive medications prescribed during the first episode, increased supply and use of medications (e.g., care giver administration of maintenance medication to children), or improved behavioural adaptations to minimize exposure in keeping with air-quality advisories, such as staying indoors and using air filters,” the researchers said in the paper. “We have previously shown that air-quality advisories reduced asthma-related emergency department visits in Toronto, Ontario.”
The smoke’s impact on adults was more sustained, the research notes.
According to the study, asthma-related hospital visits increased by up to 40 per cent among children within two days of the smoke reaching the province, while adults experienced a more sustained effect, with visits rising by as much as 48 per cent that lasted a week.
Meanwhile, adults aged 65 and above showed a “more modest and delayed increase” in daily asthma visits during the first bout of fire in early June, compared with the younger cohorts, the study found. The study suggests less outdoor exposure for older people as well as young children could explain the difference.
In 2023, Ontario experienced more than 700 fires, with 441,000 hectares of forests — slightly larger than Prince Edward Island — burned between April and October. That was almost three times more than the 10-year average, according to provincial data. The wildfires were so severe that the province sought help from firefighters from the U.S. and Mexico.
“Many Ontarians still consider wildfires to be exceptional,” Chen told CTVNews.ca in a phone interview. “Unfortunately, the 2023 wildfire will not be the last that people in Ontario and other parts of the country experience.”
The study adds that many Ontarians appeared unprepared for the unprecedented wildfires that year, a factor that may have contributed to the increase in asthma-related hospital visits.
“Ontario’s population was unaccustomed to heavy wildfire smoke episodes and was therefore unlikely to have adopted anticipatory measures or behaviours that could confound associations with health outcomes,” the study suggests.
If there’s one thing Ontarians can do to reduce health risks from wildfires, Chen told CTVNews.ca, it is to limit exposure to outdoor activities as much as possible. “No exposure to wildfires is completely safe,” he said.
