Listen: Fires Outside, Virus Inside

How wildfires make the virus more dangerous

While in California, Katherine Wells has been wearing two masks—one for the coronavirus, and one for the wildfire smoke—but she isn’t sure how to interpret the air-quality warnings. James Hamblin, her co-host on the podcast Social Distance, wants to know how air pollution such as smoke interacts with COVID-19.

They called John Balmes, a pulmonologist who has studied inhaled pollutants for decades and serves as the physician member of the California Air Resources Board. Listen to their conversation here:

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Here is a transcript of their conversation, edited and condensed for clarity:

Katherine Wells: I know there have been summers with some of these elements before, but is this surprising to you?

John Balmes: Well, yes and no. It’s certainly the worst air quality I’ve experienced since I moved to the Bay Area in 1986. But it doesn’t really surprise me. This wildfire season was predicted to be particularly bad because of the drought we had. And it was predicted to be hot and dry this summer. What was unexpected were the lightning strikes.

Wells: Last week, that orange day was surreal. What was your experience of that as a person living there?

Balmes: Well, you know, I’m a big Tolkien fan, so it seemed like Mordor that day. The sun looked like the Evil Eye of Sauron. The air quality wasn’t even that bad that day, though, because that light was [created by] the smoke plume up high blocking out the sun. We had heavy fog in the marine layer protecting the air we breathe from being really bad. It wasn’t good, but it was actually Friday of last week where there was more sun but the air quality got into “purple,” very unhealthy for everyone.

Wells: When you say purple … I’ve come out to California just recently and the air-quality indicators are all new to me. Can you orient me a little bit?

Balmes: Sure. Your listeners should get familiar with … That will give the air-quality index (AQI) for your location. Zero to 50 is green, and that’s healthy air. Fifty-one to 100 is yellow. That’s moderate, which can start to be a problem for people with preexisting lung disease or heart disease. One hundred and one to 150 is orange, and that’s when it’s especially harmful to people with preexisting heart and lung disease.

At 151 to 200—red—it becomes unhealthy for everyone. Even people without heart and lung disease may experience symptoms. And then 201 to 300, that’s purple. That’s definitely unhealthy for everyone at that point. Even healthy people are advised not to exercise outdoors. Most healthy people will not experience symptoms in the red zone.

James Hamblin: And with the AQI, when you talk about people getting sick, you’re talking about having short-term symptoms versus having long-term effects from levels of exposure?

Balmes: Yes, the AQI is focused on short-term effects, but those short-term effects can be serious for people with preexisting lung and heart disease.

Wells: That is really good to know. I spent a couple of hours outside at 150 and now I feel like I have a cold.

Balmes: That could be related to being outside in the bad air quality. One of the risk factors for smoke exposure is an increased risk of lower-respiratory-tract infections. That’s acute bronchitis and pneumonia, which is particularly problematic in the midst of the COVID-19 pandemic.

Hamblin: Does it increase your risk of having more severe disease once you’ve been infected if you’ve been living in a place that has high levels of exposure to particulate matter versus someplace else?

Balmes: Yes, there’s a building evidence with regard to air pollution, and particulate matter in particular, and COVID-19. The best-studied association is severity of COVID-19, including one study out of Harvard that I believe is actually getting published just this week, where they looked at county-level data. Counties with more chronic exposure to PM2.5—particulates that are 2.5 microns or smaller—had more COVID-19 deaths.

And that’s chronic exposure, not acute heavy exposure. But other studies from China and Italy, for example, suggest that short-term levels of PM2.5 do increase the risk of severe COVID-19. What is less clearly understood, but there are some studies that are suggestive, is whether exposure to air pollution, and particulate matter in particular, increases your risk of getting the infection. There are good reasons to suspect that it would increase your risk of infection, but that’s not been as well established as the severity of COVID-19.

Hamblin: And what most people are really afraid of is getting a severe case. And you’re talking about where the air-quality index might be on the low or safe side, but people have just been chronically exposed to it; that’s the sort of effect that might put you at risk of more severe COVID-19 if you do contract the virus.

Balmes: Yes. The Harvard study—that was actually surprising, because that was a U.S. study. It’s not in New Delhi. It wasn’t during wildfire season. U.S. PM2.5 levels aren’t that bad compared to many other parts of the world. And there was still an increased risk. There was an 8 percent increased risk for every one microgram per meter cubed—that’s the unit of measurement of PM2.5. And that was actually a pretty strong effect.

Hamblin: Wow.

Wells: In terms of practical advice for how to handle this, even if it goes on for a month, you can get an air purifier, you can not go outside. But if you live in an area that has even slightly elevated air pollution for years, I mean … Have you spent time in communities with elevated air pollution?

Balmes: I’ve done research all over the world with regard to air pollution and have been in India, for example, and in cities in Africa where there is often a lot of biomass smoke from cooking on solid fuels outdoors. We do know a lot about chronic exposure to PM2.5. And there are all sorts of health effects related to that exposure. The Global Burden of Disease, which comes out every couple of years, has listed PM2.5 as the most important environmental risk factor for death and disability worldwide. And in places like India, it’s a huge component of disease burden.

In terms of wildfire smoke, we just don’t have those kinds of chronic-exposure studies, because the community hasn’t been exposed chronically before. In general, that’s not entirely true there. There was an air inversion in Northern California over the Yurok Reservation. They had bad air for, like, a month. And the CDC actually used that to study whether masks and air purifiers helped with regard to respiratory symptoms.

And that study showed that if people stayed indoors, they did better. It also showed that the HEPA air purifiers worked. What they found, somewhat surprisingly, was wearing a respirator like an N95—I think they weren’t officially N95s then—but wearing a respirator didn’t actually protect you.

Wells: What?

Balmes: Their feeling was that people went outdoors thinking they could spend as much time as they wanted … That was the hand-waving answer to why that might have occurred. We do know that N95s protect people from wildfire smoke. Unfortunately, cloth masks don’t. Cloth masks, which we’re wearing to protect others from the wearer transmitting the virus, work for that. But they don’t protect against inhaling fine particles, because those 2.5-microns-size particles go right through the weave of a cloth mask.

A surgical mask is better. That will get you about 20 to 30 percent reduction in wildfire smoke, PM2.5. But an N95 will get 95 percent reduction if it fits you properly. And even if you haven’t been properly fitted, it probably will give you 80 percent reduction or so. The trouble is, N95s aren’t necessarily available to the general public now, because of their reservation for health-care workers and other first responders. But a type of N95 that is available is an N95 with an exhalation valve, which is actually more comfortable to wear.

Wells: Right, so I have one of those, but I’ve been wearing that. And then a cloth mask over it for COVID-19.

Balmes: Perfect. You’re great. That’s the way you should do it.

Wells: But it’s not comfortable! [Laughs.]

Balmes: [Laughs.] I didn’t say it was comfortable. But it protects you and it protects others.

Wells: I want to protect everyone and also be comfortable at the same time. But it doesn’t seem like that’s going to be the case.

Balmes: I can tell you that if you’re just walking, you don’t have to worry about infecting others with an N95 with an exhalation valve.

Wells: Oh, really?

Balmes: You have to breathe hard enough to open the valve. If you’re exercising—if you’re jogging or cycling—that will open the valve. If you’re just walking, it won’t. As a matter of fact, we’re trying to get the CDC to not be so strict about the use of N95s with exhalation valves for the public. I’m totally fine with health-care workers not using them, but, you know, there’s a grocery store that won’t let me in unless I put masking tape on or wear another mask over it.

Wells: With an N95 with masking tape over the mouth and an orange sky, you’re painting a vivid picture. So just to sum up: What do we need to know about air quality and COVID-19?

Balmes: We think that there is an increased risk of COVID-19 with poor air quality, and that includes poor air quality due to wildfire smoke, and so people should try to reduce their exposure as much as possible. And the best thing to do is to stay indoors with the windows closed and portable air cleaners in any room that they want to spend a lot of time in.