Smoke from wildfires may have added over 700 COVID-19 deaths to US toll

More than 19,742 COVID-19 cases are associated with spike in PM 2.5 levels due to wildfires 

By Susan Chacko,
Published: Wednesday 18 August 2021

Short-term exposure to smoke from wildfires in western United States of America may have caused a spike in the novel coronavirus disease (COVID-19) cases and deaths in the country, a new study suggested. 

The overall number of COVID-19 cases and deaths attributable to daily increase in particulate matter (PM) 2.5 from wildfires is 19,742 and 748 respectively, according to the report.

The findings of the study by scientists from universities across US was published August 13, 2021 in a paper titled Excess of COVID-19 cases and deaths due to fine particulate matter exposure during the 2020 wildfires in the United States.

The daily COVID-19 case and death rates were also higher on wildfire days compared to non-wildfire days, the research found. 

Over 10 million acres of land was burnt in the western United States as of December 2020. Smoke emanated from the burning forests is thick with PM2.5 that are very fine and easily penetrate lungs and other vital organs. 

PM 2.5 levels on wildfire days reached historic highs: Mono County in California experienced four consecutive days with PM 2.5 levels breaching the 500 microgram per cubic metre. This toxic pollution was caused by the Creek Fire on September 14-17, 2020. 

Wildfires are responsible for up to 25 per cent of the PM2.5 concentration in recent years across the United States and up to half in some regions of western US. 

There is a distinct correlation between short-term exposure to PM10 and PM2.5 and daily cardiovascular and respiratory mortality in 600 cities across the globe, according to a 2019 study published in New England Journal of Medicine

The study was conducted in 92 counties across California, Washington and Oregon between March 15, 2020 and December 16, 2020.

On heavy wildfire days in 2020, PM 2.5 levels were much higher than the same days in the preceding year.  This led to additional COVID-19 infections and deaths in many of the counties studied, as mentioned in the paper.

Francesca Dominici, Clarence James Gamble Professor of Biostatistics, population and data science at Harvard Chan School and senior author of the study, said:

The year 2020 brought unimaginable challenges in public health, with the convergence of the COVID-19 pandemic and wildfires across the western United States. In this study we are providing evidence that climate change — which increases the frequency and the intensity of wildfires — and the pandemic are a disastrous combination.

In the last four years, US experienced record-breaking wildfires, leading to an increase of more than 470,000 daily exposures per year and 1.85 billion more person-days of exposure to high wildfire risk compared to 2001–2004, the report mentioned. 

The study is the first to quantify the degree to which increases in PM 2.5 during the wildfires contributed to COVID-19 cases and deaths in the United States.

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