Researchers report link between exposure to wildfire smoke, increased COVID-19 cases
TORONTO -- As wildfires continue to rage across the western United States and Canada, a recent study has found that wildfire smoke is positively correlated with an increase in COVID-19 cases.
Researchers from the Desert Research Institute in Reno, Nev. published their findings on July 13 in the Journal of Exposure Science & Environmental Epidemiology. The team measured the presence of PM2.5, which refers to fine particulate pollutants that are 2.5 micrometres and smaller, and compared it with COVID-19 test data at a local hospital from May to October 2020.
Between Aug. 15 and Oct. 10, 2020, Reno was blanketed with smoke from nearby wildfires in the U.S. West and saw a significant increase in PM2.5 concentration. During this time, researchers observed a 17.7 per cent increase in the number of COVID-19 cases.
The researchers calculated that a 10-microgram-per-cubic-metre increase in the 7-day average PM2.5 concentration was associated with a 6.3 per cent increase in the COVID-19 positivity rate.
In 2020, Reno saw elevated levels of PM2.5 for a much longer period of time than most urban areas in the western U.S., making the city an ideal place for the study. The northern Nevada city saw 43 days of elevated PM2.5, levels while the San Francisco Bay Area only saw 26 days.
"We had a unique situation here in Reno last year where we were exposed to wildfire smoke more often than many other areas, including the Bay Area," co-lead author Gai Elhanan in a news release. "We are located in an intermountain valley that restricts the dispersion of pollutants and possibly increases the magnitude of exposure, which makes it even more important for us to understand smoke impacts on human health."
The researchers suggest that the increased infectivity from the wildfire smoke may be due to the way exposure to PM2.5 affects the human body. Previous studies have demonstrated that exposure to PM2.5 can induce cellular changes, which could negatively affect immune response and make COVID-19 infection easier. The particles themselves may also be potentially able to carry the SARS-CoV-2 virus, the researchers say.
However, the researchers also suggest that there may be non-biological factors. Poor air quality could encourage people to gather indoors rather than outdoors and increase the spread of the virus that way.
This study adds to the growing body of research linking high concentrations of fine particulate matter with COVID-19. Researchers from Switzerland reported last November that high levels of PM2.5 in European cities due to dust storms from the Sahara Desert were also linked with higher COVID-19 cases. Another study from U.S. researchers last August found that long-term exposure to PM2.5 "renders a population more susceptible to COVID-19."
In addition, a study from University of British Columbia researchers in June found that exposure to PM2.5 can make COVID-19 symptoms more severe.
The Reno researchers say that policymakers should consider lowering the recommended healthy limit of PM2.5 in areas with high COVID-19 cases, establish "clean air" shelters with social distancing for when air quality becomes poor and ensure that there are enough respirators in areas that have a high risk of wildfires.
"We believe that our study greatly strengthens the evidence that wildfire smoke can enhance the spread of SARS-CoV-2," Elhanan said. "We would love public health officials across the U.S. to be a lot more aware of this because there are things we can do in terms of public preparedness in the community to allow people to escape smoke during wildfire events."