Where's there's smoke, there's COVID, new study finds

The study, published in the Journal of Exposure Science and Environmental Epidemiology, examined whether fine particulate matter (PM2.5) from wildfires which hit Nevada in the summer of 2020 was associated with an increased rate of SARS-CoV-2 infections.

The researchers found a large increase (17.7%) in positive coronavirus tests at the Renown Health healthcare network in Reno, Nevada during periods of elevated PM2.5 from wildfires between August 16 and October 10 of last year.

The researchers stressed that their findings bolster arguments that other sources of PM2.5 could lead to increased susceptibility to the novel coronavirus, as well. Past studies from around the world have found associations between elevated levels of air pollution and increased infectivity and severity of COVID-19.

The increased susceptibility to the virus associated with PM2.5 could come from a number of different causes.

One possible cause is that PM2.5 increases susceptibility to respiratory viruses through modified immune responses, including inflammation. The wildfire smoke may have also helped the virus survive and spread more, as it has been shown that small particulates can increase the spread and survival of bacterial, fungal and viral bioaerosols.

Another possible cause is that elevated concentrations of ambient nitrogen dioxide (NO2) and PM2.5 result in over-expression of the ACE2 receptor, the receptor through which the coronavirus enters cells, in the respiratory tract. It is unclear whether such an effect occurs over short-term or just long-term exposure to air pollution.

The researchers noted that infection rates may also be affected by non-biological factors, such as people gathering indoors instead of outdoors due to the smoke. Policy decisions concerning whether to keep indoor public spaces open or not could have an effect as well.

The study found that PM2.5 concentrations tended to cause increased positivity rates two to six days after the concentrations were recorded, indicating a relatively short-term cumulative effect of PM2.5 from wildfires on COVID-19 rates.

“Our results showed a substantial increase in the COVID-19 positivity rate in Reno during a time when we were affected by heavy wildfire smoke from California wildfires,” said Daniel Kiser, MS, co-lead author of the study and assistant research scientist of data science at DRI, according to DRI. “This is important to be aware of as we are already confronting heavy wildfire smoke from the Beckwourth Complex fire and with COVID-19 cases again rising in Nevada and other parts of the Western US.”