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How California's atmospheric rains are increasing cases of Valley fever

The atmospheric rivers that’ve pummeled California this winter have caused flooding, mudslides and other impacts.

But the phenomenon is also leading to an increase in Valley fever cases in that state. Health officials say last year set a new record for the most new cases in a year.

Zoya Teirstein is a staff writer at the environmental magazine Grist, where she covers climate change and human health. She’s written about this and joins The Show to talk more about it.

Full interview

MARK BRODIE: And so what is the relationship between these atmospheric rivers and the fungus that causes Valley fever?

ZOYA TEIRSTEIN: Well, so the fungus, I mean, if you've ever been mushroom hunting or, or seen mushrooms growing, you know that they love water. They really, there, there's these flushes that kind of come out of the ground whenever there's a lot of water. That's why mushrooms are prevalent in the fall mainly and spring. And what happens is that, you know, this fungus that causes this really dangerous infection for some people, called Valley fever, responds much the same way when there's a lot of water, it flourishes. And then the tricky part is that when it's very dry, it dries out, and this fungus is microscopic. So the spores are tiny, tiny, you can't see them with the naked eye, they get lifted into the air. If you breathe them in, that's when the, the infection can occur.

BRODIE: So, is the issue just with the quantity of water that California is getting right now, followed by what we imagine will be another dry summer. 

TEIRSTEIN: That's exactly right. And so some listeners might be wondering, well, why is climate change a factor? How does it, you know, have to do with this? And the truth of the matter is that Valley fever has been around for a long time. It is not a new phenomenon. It was discovered more than a century ago, and the climate connection is really just sort of an overlay on top of existing factors. So when it's very wet, as you said, and then very dry, that cycle contributes to more cases of the infection. And so what you're seeing now are these extraordinarily wet winters for California. It's no coincidence that Arizona is the state, by the way, that has the most cases of Valley fever, about two-thirds of the cases that happen every year occurring in Arizona. And if you look at the way that Arizona's winter and summer go, it's, you know, get the monsoon season, it's very wet and then all of a sudden it's very, very dry. And a similar, you know, climatic cycle is unfolding in California. It wasn't always the case that California got atmospheric river after atmospheric river, one after another sort of dumping huge quantities, you know, millions and millions of gallons of water on the state and then having these like extraordinarily hot summers. But that is the sort of status quo now, it, it's been emerging in recent years.

BRODIE: So is the situation in California then just sort of becoming what it has generally been in Arizona?

TEIRSTEIN: You know, no researcher has said those exact words to me, that's me extrapolating from what I'm I'm hearing, you know, and seeing on the ground in terms of data. But I think that it's an, it's an OK analogy to make. There are similar climatic conditions unfolding in California. And so you can see it's, it's no coincidence that the wet-dry cycle that Arizona sees every year being replicated in California is now leading to more cases of this infection. 

BRODIE: There, there's also, I assume, an implication from all of the development going on in California, building. You know, they, you know, LA and other parts of California like in Arizona have has a shortage of housing and affordable housing. There's always more development happening and, you know, when that construction comes in and kicks up the dust and, you know, digs deep enough to get to the spores that can release it into the air, I would assume that that plays a pretty significant role in California as well.

TEIRSTEIN: Yeah, that is exactly right. So, it's never, just climate change, never acts in a vacuum. It's always climate change and other factors or just other factors point blank. And that development into sort of virgin areas of, of the state of California, much like in Arizona is, is certainly a major factor. I mean, if you look at some of these construction zones, what they'll do during the week is they'll spray water to tamp down dust. But over the weekend, as one told me, those sites will, will get very dry and the wind will blow and the dust will go everywhere. And that is one of the ways in which Valley fever gets spread around. 

BRODIE: So how big of an increase in cases are health officials in California seeing? 

TEIRSTEIN: Well, health officials in California have seen a, you know, a 10-fold increase in cases in the past couple of decades. And that isn't that, you know, that the rate of growth, as I said, Arizona still has more cases in California in a year, but the rate of growth is higher in California. And that's definitely notable.

BRODIE: And some of that as you report is due to the fact that people are more aware of Valley fever, they're more reliable tests for it now. But as at least one source told you that that's not explaining all of this.

TEIRSTEIN: No, and that's, that's where the climate factor comes in. You've got these weather patterns that are looking a lot like Arizona and you've got, you know, very, very dry summers plus development. Plus, you know, more testing, plus, plus more public awareness. And so you've got these cases, I mean, nearly 10,000 cases in California in 2023. And experts said that 2024 will be likely more of the same.

BRODIE: So what do health officials in California say can be done about this? I mean, obviously you can't stop the rain from falling and you can't really stop California from being hot and dry in the summer. So like what's the answer here?

TEIRSTEIN: Yeah, that's, that's where things get tricky and I wish I had better answers. There's a vaccine in development for dogs. And hopefully one day there'll be one for humans, too. More public awareness, it is really crucial. The truth of the matter is is that the way that your immune system responds to the infection. It is most of the battle. So people who are immunocompromised are more at risk for developing the the severe forms of Valley fever. There's also some strange ethnic discrepancies like Filipinos, Native Americans are more susceptible. Black people are more susceptible. Researchers are still trying to figure out why that might be. But more public awareness I believe is sort of the, the the first foray in keeping this, this infection at bay. The tricky thing is that, of course, if you're a state like Arizona, this is something I've been told by experts that I've spoken to in the state, you know, you don't want to really advertise that you have this scary fungal pathogen sort of roaming around, you know. So I think states in general could be doing more to get ahead of what is a growing problem. 

BRODIE: Well, and as you reference, health officials in California say that 2024 could be even bigger for Valley fever than 2023. Looking beyond just this year, assuming that the, the climate situation, the weather situation stays as it is. Is there any reason to think it won't continue just to grow exponentially year over year?

TEIRSTEIN: No, I mean, the thing about Valley fever, about these spores is that they are sensitive to you know, to too much water to too much heat and drought. So if it gets too, too dry or very, very, very wet, the spores don't really proliferate. They love the boom bust cycle that that happens in Arizona and now California. So it's tricky to predict. But what one researcher found is that if emissions get very high by the end of the century, and continue being very, very high throughout the next, you know, decades, then much of the Western United States will become endemic to Valley fever. So we're talking you know, Oregon and Washington largely, too. Right now, there are, there have been some isolated cases in those states, which is an indication that the disease is that the infection is spreading. But it, you know, it's not as widespread, of course, as it is in, in California or Arizona.

BRODIE: All right. That is Zoya Teirstein, a staff writer at Grist. Zoya, thank you so much. I really appreciate it.

TEIRSTEIN: Thanks so much for help.

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Mark Brodie is a co-host of The Show, KJZZ’s locally produced news magazine. Since starting at KJZZ in 2002, Brodie has been a host, reporter and producer, including several years covering the Arizona Legislature, based at the Capitol.