SACRAMENTO, Calif. — Cases of COVID-19 rose sharply last year in Reno, Nevada, when heavy layer of wildfire smoke settled over the city, according to scientists at the Desert Research Institute, and they and other scientists are postulating that there is a link between air pollution and increased susceptibility to the new coronavirus.

“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, a co-lead author of the study published in the Journal of Exposure Science and Environmental Epidemiology. “This is important to be aware of as we are already confronting heavy wildfire smoke … with COVID-19 cases again rising in Nevada and other parts of the western U.S.”

Kiser, an assistant research scientist of data science at the institute, said he became interested in studying the effect of the microscopic particulate matter from wildfires after reading a Canadian scientist’s article on the dual effect of confronting both issues at the same time.

(Jennifer Luxton / The Seattle Times)
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In the preface to her work, senior scientist Sarah Henderson of the British Columbia Center for Disease Control, wrote: “As we enter the wildfire season in the northern hemisphere, the potential for a dangerous interaction between SARS-CoV-2 and smoke pollution should be recognized and acknowledged. This is challenging because the public health threat of COVID-19 is immediate and clear, whereas the public health threat of wildfire smoke seems distant and uncertain in comparison. However, we must start preparing now to effectively manage the combination of public health threats.”

Kiser is hoping that his research results will motivate people to get vaccinated and to wear masks to reduce their exposure to the virus and to tiny wildfire particulate matter that measures 2.5 micrometers or less.


That’s about 1/30th the size of a human hair at its largest. Scientists refer to it as PM 2.5 for short.

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To analyze the relationship between this fine wildfire ash and COVID-19 positivity rates, Kiser and his team collected data from the Washoe County Health District and the region’s big hospital system, Renown Health.

He said they discovered that the PM 2.5 was responsible for a 17.7% increase in the number of COVID-19 cases that occurred during a period of prolonged smoke that took place between Aug. 16, 2020, and Oct. 10, 2020.

Washoe County’s 450,000 residents, many of whom live in Reno, experienced 43 days of elevated PM 2.5 during that period, researchers said, compared with 26 days for residents of the San Francisco Bay Area.

“We had a unique situation here in Reno last year where we were exposed to wildfire smoke more often than many other areas, including the Bay Area,” said Dr. Gai Elhanan, co-lead author of the study and an associate research scientist of computer science at the institute. “We are located in an intermountain valley that restricts the dispersion of pollutants and possibly increases the magnitude of exposure, which makes it even more important for us to understand smoke impacts on human health.”


The relationship between COVID-19 positivity rates and air pollution in general has gained interest among scientists around the world, and Kiser and Elhanan cite research papers from Europe and Asia that explore the phenomenon as well.

Kent Pinkerton, an expert on air pollution on the faculty at the University of California, Davis, said there’s concern among physicians and scientists about the impact of climate change on cardiopulmonary health, a topic he’s currently addressing in an article he’s submitting to a medical journal.

“Hotter temperatures, climate change, wildfires, air pollution, all seem to have some association with a greater risk of COVID-19 cases,” Pinkerton said. “If you’re susceptible to air pollution, such as particulate matter, it could be that you just have a situation where you’ll be also much more susceptible to viral particles that might be in the air that you’re breathing. It’s not that the air pollution makes the COVID-19 cases more likely to happen, but it may simply be a reflection of just the fact that, where areas of high pollution are,…the risk for COVID-19 cases may be greater. “

Pinkerton said he read a paper on a study out of Turkey, which was submitted to a medical journal, and researchers there also found a terrible upswing in COVID-19 cases linked to increased air pollution..

No one has yet found the mechanism that increases the risk, Kiser and Pinkerton said, but there have been some hypotheses.

Could the new coronavirus be hitching rides on the PM 2.5 and managing to remain virulent as it is breathed into people’s lungs? Certainly, PM 2.5 has been found in the smallest air sacs of people’s lungs.


Kiser’s team cites a study out of Northern Italy where researchers found the new coronavirus on particulate matter, and Pinkerton noted that the pathogen has been detected in water supplies and in sewage.

“We know that dust from the Mongolian desert, that comes across the Pacific Ocean, can carry at least biological material, whether it be viral or bacterial,” Pinkerton said. “What people have argued about is that the dust can be a carrier for microorganisms.”

It raises questions, Pinkerton added, of how long a virus can survive.

Kiser and Pinkerton said researchers also have postulated that the PM 2.5 irritates nasal, throat and lung passages, creating inflammation that makes those areas ripe for infection. Some research has even suggested that the PM 2.5 increases the presence of a histamine receptor to which the COVID-19 virus attaches, Kiser said.

Elhanan said: “We believe that our study greatly strengthens the evidence that wildfire smoke can enhance the spread of SARS-CoV-2. We would love public health officials across the U.S. to be a lot more aware of this because there are things we can do in terms of public preparedness in the community to allow people to escape smoke during wildfire events.”

In fact, the U.S. Centers for Disease Control and Prevention have a website about wildfire smoke and COVID-19 that provides tips on how to prepare for wildfire season, including identifying high-efficiency air filters and maintaining a supply of N95 respirators which filter out particulates.