Small particulate matter pollution in wildfire smoke in the western United States increases the risk for COVID-19 infection and death from the disease in people living in affected regions, a study published Friday by Science Advances found.
Nearly 20,000 COVID-19 cases and 750 deaths in California, Oregon and Washington between March and December of last year may be linked with a rise in fine particulate air pollution, or PM2.5, generated by the wildfires plaguing the region, the researchers 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,” study co-author Francesca Dominici said in a press release.
“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,” said Dominici, a professor of biostatistics, population and data science at the Harvard T.H. Chan School of Public Health in Boston.
Like all sources of air pollution, wildfires produce high levels of PM2.5, which are microscopic particles invisible to the naked eye, according to the researchers.
Exposure to these particles causes significant health problems, including asthma, chronic obstructive pulmonary diseases and other respiratory illnesses, and can be deadly, research suggests.
In addition, in a study presented in July during the European Congress of Clinical Microbiology & Infectious Diseases, researchers found a link between short- and long-term exposure to PM2.5 and COVID-19 risk.
For this analysis, Dominici and her colleagues designed a statistical model to quantify the extent to which wildfire smoke may have contributed to excess COVID-19 cases and deaths in California, Oregon and Washington, the three states that bore the brunt of the wildfires across the west last year.
They hoped to identify any potential connection between county- and daily-level data on PM2.5 air concentrations from monitoring data, wildfire days from satellite data and the number of COVID-19 cases and deaths in 92 counties, which represented 95% of the population across the three states, they said.
The analysis accounted for factors such as weather, population size and societal patterns of social distancing and mass gatherings, according to the researchers.
When wildfire activity was at its highest in the region, from August 15 to October 15 of last year, daily levels of PM2.5 during wildfire days were about five times higher than it was on non-wildfire days, the data showed.
In some counties, daily PM2.5 levels on wildfire days reached up to 80 times those of non-wildfire days, the researchers said.
On average across all counties, a daily increase of 10 micrograms per cubic meter of air in PM2.5 each day for 28 subsequent days was associated with a 12% increase in COVID-19 cases and an 8% rise in deaths caused by the virus, the data showed.
Whitman County, Wash., saw the highest increase in PM2.5-linked virus cases in the study, at 72%, while San Bernardino County, Calif., had the highest rise in deaths, at 66%.
Whitman also had the highest percentages of total COVID-19 cases attributable to high levels of PM2.5 during the wildfires, at just over 18%, while 41% of virus deaths in Butte County, Calif. were attributable to high levels of PM2.5 during the wildfires, they said.
“Climate change will likely bring warmer and drier conditions to the West, providing more fuel for fires to consume and further enhancing fire activity,” Dominici said.
“This study provides policymakers with key information regarding how the effects of one global crisis, climate change, can have cascading effects on concurrent global crises-in this case, the COVID-19 pandemic,” she said.