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Study: Wildfire Smoke Led To 18% Rise In COVID-19 Cases

A wildfire burning alongside the top of a forest land
Courtesy of National Interagency Fire Center
Plumes of smoke rise off the Warm Fire, which burned in the Boise National Forest in July 2020. A new study suggests a causal link between wildfire smoke and a rise in COVID-19 cases.

COVID-19 cases rose by an estimated 18% during a period when heavy wildfire smoke blanketed the Reno area. The findings suggest that the smoke from wildfires increase the rate of COVID-19 transmission.

KUNR Morning Edition host Noah Glick spoke with Daniel Kiser, an assistant research scientist with the Desert Research Institute and the co-lead author of the new study, to learn more.

Noah Glick: Eighteen percent. That sounds pretty significant. Can you tell me more about what you studied and what you found?

Daniel Kiser: Daniel Kiser: Our interest in this research question was peaked when we read an article by Sarah Henderson, which was published in early 2020 that basically predicted, based on studies that had been done on air pollution in general, say in Europe, and just the association that they found between COVID cases and air pollution, that if we had a really bad wildfire event, we might expect to see COVID cases increase because of it. So we were wanting to look into that and see if that’s what we found.

Glick: So the idea sparked from another study and looking into it. So then, what did you end up finding from your study?

Kiser: As you said, we found what appears to be a very significant association between PM2.5 and an increase in the rate of positive cases at Renown Health, which is a big hospital here in Reno. So that is equivalent to about 178 cases that we might not have otherwise have seen because of the wildfire smoke.

Glick: Let’s take a step back. You mentioned PM2.5. Can you just explain what that is? We talked about this a little bit last year with the pandemic and primarily around the topic of face masks, but let’s remind folks. What is PM2.5, and what does that mean? Why is that significant?

Kiser: PM2.5 is one of the big pollutants that wildfires produce. It’s particulate matter that’s smaller than 2.5 microns, so sometimes it’s also called fine particulate matter. So it can be very easily inhaled; it’s very fine. It can get really deep into your lungs and can be really harmful, not just for the spread of infectious diseases but for a lot of other things as well.

Glick: Can we actually link a rise in COVID for sure with this wildfire smoke? Couldn’t it be a mix of other factors, I guess? Could we see folks getting tired of being inside and wanted to go outside, the holiday gatherings we heard about over the summer? I feel like there’s a variety of factors that go into this, so can we say with certainty that wildfire[s] helped raise the number of COVID cases?

Kiser: Our study was observational. As you said, there could be other things going on that we just don’t know about, and so there’s definitely a need to be cautious in interpreting these results. I think that there are reasons to think that the effect of wildfire smoke on COVID is causal. One of them being the fact that we see a rise in cases after we see a rise in PM2.5. You would expect there to be that chronological order.

But then there’s also several theories out there of how this could be happening. One is that the virus particles actually attached to the PM2.5 particles and then gets inhaled into our lungs. So basically the PM2.5 is helping to spread the virus around.

Glick: Wildfire season is lasting longer. Smoke impacts are being felt longer. The duration, the intensity of these fires are getting bigger. Could you see a scenario where if we’re seeing prolonged periods of wildfire smoke, that could impact public health over a longer term?

Kiser: There have been lots of studies done on just the harmfulness of wildfire smoke in general. There have been indications, of course, that it plays a role in respiratory issues like asthma. It can make things like COPD worse. It might even play a role in cardiovascular issues. We would expect that with the increase in intensity in these wildfire smoke events that we’re going to see more of a public health impact. It’s kind of where all the science is pointing.

Glick: There’s a lot of talk about vaccinations right now with COVID-19, and we won’t get into the political argument about that, but can vaccinations, do they offer any sort of protection against some of these risks with COVID and wildfire smoke?

Kiser: I think one of the big takeaways that I feel like from our paper is that it’s important to both reduce your exposure to COVID-19 and also to wildfire smoke. The most efficient way to reduce your exposure to COVID-19 is to be vaccinated. It’s easy; it’s effective. And so, I think, if anything, our study would increase the urgency of that. And, of course, you also want to reduce your exposure to wildfire smoke as much as possible. Trying to avoid strenuous exercise outdoors when possible is good [and] trying to just limit your exposure to that wildfire smoke.

Daniel Kiser is an assistant research scientist with the Desert Research Institute in Reno.

Noah Glick is a former content director and host at KUNR Public Radio.
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