Wildfire smoke exposure linked to COVID-19 case increase: study

By | July 27, 2021

Wildfire smoke exposure likely contributed to an increase in Reno, Nevada’s COVID-19 cases last year, researchers suggested, noting that the findings could inform policies to tamp down harmful effects from air pollution amid the pandemic.

Exposure to tiny particles in smoke (specifically measuring 2.5 µm in diameter or smaller, PM2.5) “increases susceptibility to respiratory viruses” causes airway inflammation and boosts “the spread and survival of bacterial, fungal and viral bioaerosols,” including those containing the virus causing COVID-19, study authors wrote in findings recently published in the Journal of Exposure Science & Environmental Epidemiology.

To determine any association between exposure to wildfire smoke and an increased rate of coronavirus infections in Reno, researchers from the Desert Research Institute compiled data from the Environmental Protection Agency’s online database with several air quality monitors situated in Reno and Sparks, applied a weighted average of PM2.5 concentrations in the area each day to approximate the population’s daily exposure, gathered weather data from KRNO weather station in Reno and obtained COVID-19 test results and patient data from Renown Health, a large health system in the surrounding county. The study period began on May 15, 2020, and ended on October 20, 2020.

“Exposure to wildfire PM2.5 accounted for an additional 178 positive COVID-19 cases at Renown alone between 16 Aug and 10 Oct 2020, or an increase of 17.7 percent [in the number of cases],” authors wrote in part. During the study, over 35,000 people were tested at Renown, with 8 percent of tests returning positive. Most of the patients were over age 30, but the fastest increases in coronavirus-positive patients occurred among younger adults aged 18 to 29.  

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Air quality was affected by wildfire smoke for 59 days during our study period, with 50 of those days occurring between 16 Aug and 10 Oct 2020,” the study reads, later adding, “We found a large increase in the SARS-CoV-2 test positivity rate at Renown during periods of elevated PM2.5 from wildfires. These results, although based on observational data with their inherent limitations, lend credence to earlier predictions that wildfire smoke would exacerbate the COVID-19 pandemic. Our findings also bolster arguments that PM2.5 from other sources, such as vehicle traffic or industry, increases susceptibility to SARS-CoV-2.”

While the number of virus-related deaths was beyond the scope of the study, researchers said it was “reasonable to assume that the excess cases due to wildfire PM2.5 resulted in excess mortality.”

The study had its limitations, including potential confounding factors in other harmful compounds in wildfire smoke (like carbon monoxide, ozone and nitrogen oxides) and researchers couldn’t account for differences in exposure on an individual basis owing to jobs or income.

“Our findings should help shape regional policies that seek to manage the combined threats of wildfires and the pandemic,” authors concluded. “These policies might include lowering the recommended healthy limit for PM2.5 in cities with a high prevalence of SARS-CoV-2, establishing ‘clean air’ shelters that maintain social distancing and allocating sufficient quantities of appropriate respirators to areas at high risk for wildfires.”

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