Excess of COVID-19 cases and deaths due to fine particulate matter exposure during the 2020 wildfires in the United States.

Zhou, Xiaodan; Josey, Kevin; Kamareddine, Leila; Caine, Miah C; Liu, Tianjia; Mickley, Loretta J; Cooper, Matthew; Dominici, Francesca · Sci Adv · 2021

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Abstract

The year 2020 brought unimaginable challenges in public health, with the confluence of the COVID-19 pandemic and wildfires across the western United States. Wildfires produce high levels of fine particulate matter (PM<sub>2.5</sub>). Recent studies reported that short-term exposure to PM<sub>2.5</sub> is associated with increased risk of COVID-19 cases and deaths. We acquired and linked publicly available daily data on PM<sub>2.5</sub>, the number of COVID-19 cases and deaths, and other confounders for 92 western U.S. counties that were affected by the 2020 wildfires. We estimated the association between short-term exposure to PM<sub>2.5</sub> during the wildfires and the epidemiological dynamics of COVID-19 cases and deaths. We adjusted for several time-varying confounding factors (e.g., weather, seasonality, long-term trends, mobility, and population size). We found strong evidence that wildfires amplified the effect of short-term exposure to PM<sub>2.5</sub> on COVID-19 cases and deaths, although with substantial heterogeneity across counties.