Canadian wildfires triggered a 23.6% spike in asthma emergency visits in 2023, yet researchers discovered a surprising absence of increased visits during the second wave despite worse air quality.

At a Glance

  • Canada's 2023 wildfire season caused significant increases in asthma-related emergency department visits during the initial exposure period
  • Surprisingly, a second smoke event with higher PM2.5 levels didn't increase emergency visits, suggesting effective public health measures
  • Communities must develop better strategies including improved air quality monitoring, public health messaging, and emergency response planning
  • High-risk populations include those with pre-existing conditions, children, older adults, pregnant individuals, and outdoor workers
  • Experts recommend staying indoors, using air filters, wearing N95 masks outdoors, and limiting strenuous activity during wildfire events

Wildfire Smoke's Impact on Public Health

Canada experienced its most destructive wildfire season in 2023, with smoke from Quebec wildfires significantly deteriorating air quality across Ontario and much of North America. The environmental disaster created a natural experiment for researchers studying public health responses. Data shows the first fire event in Ontario resulted in a 23.6% increase in daily asthma-related emergency department visits, with effects lasting up to five days. These visits represented a significant strain on healthcare systems already dealing with the disaster's broader impacts. Wildfire smoke, consisting of gases and fine particles (PM2.5) from burning materials, poses substantial health risks beyond asthma, including irritation of eyes, nose, and throat, exacerbation of lung diseases, increased cardiovascular events, and potential mental health effects.

The frequency and intensity of wildfires are increasing due to climate change, making this a growing public health concern. From April 30 to August 4, 2023, millions of Americans were also exposed to smoke from these Canadian wildfires. Data from the National Syndromic Surveillance Program showed a 17% increase in asthma-related emergency visits during smoke exposure days, with increases most notable among individuals aged 18 to 64 and in regions with prolonged smoke exposure.

Unexpected Findings and Public Health Lessons

What surprised researchers was that despite higher PM2.5 exposure, the second smoke event showed no significant increase in asthma-related emergency visits. This unexpected finding suggests that protective measures taken after the first event were effective. Dr. Hong Chen of Public Health Ontario noted, "We did not observe a similar increase in asthma-associated ED visits in the second episode, compared with the first," adding that "it may have to do with some extended protection from the first to the second episode."

This suggests that effective public education, emergency preparedness, and targeted resource deployment between the two events played a crucial role in mitigating health impacts. Communities that implemented precautionary measures such as staying indoors, using air filters and masks, and limiting strenuous activity likely contributed to the reduced emergency department burden. The Environmental Protection Agency's Air Quality Index (AQI) proved valuable in correlating air quality with health risks, allowing for more targeted public health communications.

Preparing for Future Wildfire Seasons

Researchers emphasize that forecasting systems for predicting PM2.5 exposure are crucial for public awareness and preparedness. Sarah Henderson, PhD, from the BC Centre for Disease Control, noted, "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." This underscores the need for specialized response strategies specifically for wildfire smoke events rather than applying general air pollution protocols.

Health experts recommend several actions to reduce exposure during wildfire events: staying indoors with windows and doors closed, using HEPA air filters in homes, wearing N95 respirators when outdoors is necessary, reducing smoke in vehicles by keeping windows closed and using recirculated air conditioning, and protecting indoor air quality. These recommendations are particularly important for high-risk populations including those with pre-existing health conditions, children, older adults, pregnant individuals, outdoor workers, and those with limited access to healthcare or financial resources.

Building Community Resilience Through Research

The findings from the 2023 wildfire season suggest the need for future research to identify measures to mitigate health impacts of wildfire smoke and to assess long-term effects on cardiovascular and mental health. Researchers advocate for emergency response planning and targeted public health communication to prevent exacerbations, especially among vulnerable populations. "Community preparedness and appropriate and prompt response are crucial to reduce wildfire smoke exposure and morbidity," wrote researchers in one study. "Recommended actions include assessing a possible health care utilization surge related to wildfire smoke exposure."

As Chen and colleagues stated, "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." Communities need to develop better strategies to protect residents from smoke, including improved air quality monitoring networks, enhanced public health messaging, and coordinated emergency service innovation. Health researchers suggest using asthma as an indicator in syndromic surveillance to develop strategies for reducing health impacts and expanding monitoring to better understand the broader health effects of wildfire smoke.