Wildfires May Amplify Effect of PM₂.₅ Exposure on COVID-19 Dynamics

Wildfires seem to amplify the effect of short-term exposure to fine particulate matter (PM2.5) on COVID-19 cases and deaths, according to a study published online Aug. 13 in Science Advances.

Xiaodan Zhou, from the Environmental Systems Research Institute in Redlands, California, and colleagues obtained and linked publicly available daily data on PM2.5, the number of COVID-19 cases and deaths, and other confounding variables for 92 Western U.S. counties affected by wildfires in 2020. The association between short-term PM2.5 exposure during the wildfires and the epidemiological dynamics of COVID-19 cases and deaths was estimated.

The researchers found that 52 of 92 counties had strong evidence of a positive association between PM2.5 exposure and an increased risk for COVID-19 cases four weeks later. In a pooled analysis across counties, a daily increase of 10 µg/m3 in PM2.5 for 28 subsequent days was associated with an increase of 11.7 percent in COVID-19 cases. Seventeen of the 92 counties had strong evidence of a positive association between PM2.5 exposure and an increased risk for COVID-19 deaths four weeks later. Across counties, pooled distributed lag effects showed that a daily increase of 10 µg/m3 in PM2.5for 28 subsequent days was associated with an increase of 8.4 percent in COVID-19 deaths.

"Wildfires during a pandemic create a cascading disaster with disruption to directly affected communities that challenge infection mitigation practices, such as social distancing in evacuation shelters, while local disaster responses (including health care) are multiply stressed," the authors write. "These synergies likely increased COVID-19 cases and negative outcomes."