Spike in Hospital Visits for Asthma Linked to Wildfire Smoke: Study

Smoke from wildfires burning across Ontario and Quebec blanket the skyline in Kingston, Ont., on June 6, 2023. The Canadian Press/Lars Hagberg

Asthma-related emergency room visits substantially increased across Ontario during the 2023 wildfires in Canada, a new study says.

A report released by the Canadian Medical Association Journal (CMAJ) on May 5 noted that hospital visits for asthma spiked during the first wave of wildfire smoke in early June 2023. The number of visits reduced during the second episode at the end of the month.

The report noted that preemptive measures may not have been taken before the first wave, but people were more prepared by the time the second smoke episode emerged. It is likely that there was an increased supply and use of medications, as well as improved measures to minimize smoke exposure, including staying inside and using air filters, the report said.

Wildfire smoke contains air pollutants that can travel far distances and deteriorate air quality in areas of dense population. Thousands of Canadians were displaced as a result of the fire, which destroyed property and left vast areas of North America in smoke.

Environment Canada issued special air quality advisories for much of Ontario and Quebec in June 2023, and school boards in the Toronto area cancelled outdoor activities.

The May 5 report outlines a study led by Hong Chen, a Health Canada research scientist, who found that Canada’s “most destructive wildfire season on record” of 2023 significantly increased asthma-related emergency room visits across Ontario, while effects on other health conditions were less clear.

The study, which ran from about eight weeks before the first smoke episode until around four weeks after the second episode, compared daily emergency hospital visits before, during, and after the wildfire events to assess the impact of wildfire smoke. Smoke plume data showed that daily air pollutant concentration surged across Ontario during the two smoke episodes in June.

Ontario hospital data indicated that asthma-related hospital visits following the first smoke episode were higher than usual for six days after the episode, with the first and second days showing the greatest spike. Meanwhile, the second episode did not appear to lead to a significant increase in asthma-related visits.

The study examined why the first occasion of heavy smoke resulted in an increase in asthma-related problems while the second episode did not.

Ontario has rarely experienced severe wildfire smoke in its populated areas, unlike the western provinces where residents are more accustomed to dealing with smoke pollution, Chen’s report said.

Demographics

The study also looked at whether age was a factor in asthma-related hospital visits.

Chen analyzed hospital visits by age for asthma and concluded that though there were increased visits among children, a more substantial increase was seen among adults.

The report said that the increase in asthma-related hospital visits among people aged 65 and older was more modest and delayed, compared to adults aged 18 to 64 years.

“Older adults tend to spend more time indoors, whereas younger adults might choose to continue daily activities such as work, school, or errands, despite wildfire warnings during this episode,” the CMAJ report said.

The study indicated that the number of children visiting hospitals for asthma-related complications had increased as well, but not as substantially as the increase among adults.

Other studies that analyzed the 2023 Canadian wildfires and the effects smoke had on asthma showed findings that aligned with the May 5 report.

Another study by Chen, which looked at emergency department visits in New York City, found a 44 percent increase in asthma-related visits resulting from the wildfire smoke event. Meanwhile, a study by the U.S. Centers for Disease Control and Prevention analyzed data from several U.S. states and found that the 2023 Canadian wildfires led to an increase in emergency visits for asthma by 17 percent.

Past studies on previous wildfire seasons have also shown increased hospital visits for asthma as a result of wildfire smoke exposure.

Wildfires in California in 2003 resulted in significantly increased hospital visits for respiratory complications, especially asthma, said an Occupational and Environmental Medicine study from BMJ Journals. Similar findings came from a study on the 2007 California wildfires.