The Cabin in Mammoth Lakes

Rachel:
A small ski town in California. Mammoth Lakes. Population, seven thousand. Mostly tourists, year-round.

In February of twenty twenty-five, a resident is admitted to the local hospital with what looks like severe flu. The doctors there have been seeing this disease since nineteen ninety three. They know the protocol. They try everything in the protocol.

The person dies.

In March, a second resident of Mammoth Lakes dies of the same disease.

In April, a third. A twenty-six-year-old who worked at one of the hotels.

The public-health investigators go through the homes, looking for the pattern they have learned to look for over the last thirty years.

In one of the three, they find it. Mice in the kitchen. Mice in the storage. Textbook hantavirus exposure.

In the other two, they find nothing. No mice. No droppings. No nests.

So how did those two get it.

From Armbrust USA, this is Vector. Season one. Hantavirus. Episode two.

I'm Rachel Marin. With me is Seth Avery.

Seth:
Hantavirus is a rodent disease. The Sin Nombre strain in the Western United States kills about a third of the people it infects.

Rachel:
It is back. This is the place where it is loudest right now.

Rachel:
Mammoth Lakes is in Mono County, on the eastern slope of the Sierra Nevada. About six hours north of Los Angeles, four hours south of Reno. It is a ski town. The lifts run from November through May. In summer, hikers and trail runners replace the skiers. The permanent population is around seven thousand, but on a busy weekend the town swells to forty thousand.

Seth:
Mono County is also the hantavirus capital of California. The state has logged about ninety-nine Sin Nombre cases between nineteen eighty and twenty twenty-five. Mono County alone accounts for twenty-seven of them. That is more than any other county in the state. The Sierra Nevada is home to the deer mouse, peromyscus maniculatus, which is one of the primary carriers of Sin Nombre, the original American hantavirus strain. The cabins, the woodpiles, the storage sheds, the seasonal housing where ski-resort workers live, those are exactly the environments deer mice like.

Rachel:
When Mono County announced the first death of twenty twenty-five on February twenty seventh, the local health officer, Dr. Tom Boo, called the case uncommon but extremely dangerous.

Seth:
The second death, on March twenty sixth, prompted the county to expand its outreach and screening.

Rachel:
And then the third, on April third. Dr. Boo's statement on that one had a different tone. He called the cluster, quote, "tragic and alarming." He admitted the county did not have a clear sense of where this young adult had contracted the virus.

Seth:
That is the line that the public-health community noticed. Because in all three cases, none of the victims had engaged in the kind of high-risk activity that the disease is normally associated with. They had not been cleaning out poorly ventilated outbuildings full of mouse waste. They had been, in Dr. Boo's words, going about normal daily activities.

Rachel:
The national press picked up the story on April sixth. By the end of that week the cluster was being framed everywhere through the celebrity death that had happened a few weeks earlier. We will come back to that next episode.

Seth:
What was unprecedented was the timing. Hantavirus cases in the Sierra typically peak in late spring and summer. The deer mouse population breeds when it gets warm. February is too early for the usual exposure profile.

Rachel:
And it wasn't just one case. It was three. In four months. Each in a person who lived and worked in Mammoth Lakes.

Seth:
For a county that has averaged less than one case a year for thirty-two years, three in a single quarter is a signal.

Rachel:
You might be wondering, why does this small town in California keep getting hantavirus cases when most of the country goes years without one.

Seth:
A few overlapping reasons. One. The Sierra Nevada deer mouse carries Sin Nombre virus, and its range covers the entire eastern Sierra and Great Basin. Mono County is dense with it. Two. Mammoth Lakes is full of exactly the kind of buildings where exposure happens. Vacation cabins that sit closed for weeks at a time. Employee housing for seasonal ski-resort workers. Storage sheds and barns and woodpiles. Each of those is a place a deer mouse will set up a nest, and a place a human will eventually walk into and disturb the dust.

Rachel:
There is a precedent for this, and it is worth pulling up.

Seth:
In the summer of twenty twelve, ten visitors to Yosemite National Park were diagnosed with hantavirus. Three of them died. Nine of the ten had stayed in what were called the signature tent cabins at Curry Village. The cabins had been built three years earlier with an insulating layer of foam and drywall between the canvas and the interior. The deer mice loved it. They moved into the walls. Investigators traced the outbreak directly to those specific cabins. The signature tent cabins were demolished.

Rachel:
The relevant detail for our story is not the Yosemite outbreak itself. It is the lesson. When a structure is designed to be warm and enclosed and seasonal, and there is a local deer mouse population, those two things eventually find each other.

Seth:
Three. Mammoth Lakes has hundreds of short-term rental units. Every Saturday in winter, dozens of cabins turn over. Someone leaves, someone cleans, someone else arrives. The cleaners are the ones at risk.

Rachel:
We talked about this in episode one. The rule is not that hantavirus is everywhere. The rule is that the places it shows up have a pattern. Cabins. Sheds. Garages. Seasonal housing. Mammoth Lakes has all of those, at scale, all the time.

Seth:
The town has lived with this for thirty-two years. The local hospital knows the symptoms. The county health department has informational pamphlets. The ski resorts brief their seasonal workers. That groundwork is part of why the twenty twenty-five cluster was caught. They saw the first patient and knew exactly what they were looking at.

Rachel:
The question that has emerged is not whether the system worked. It did. The question is what changed.

Seth:
Here is the wrinkle. In one of the three twenty twenty-five cases, the patient's home had a significant rodent problem. Mice in the kitchen, mice in storage, mice in the laundry. That is a textbook exposure environment. In the other two cases, the public health investigators found no evidence of mice in the home at all.

Rachel:
None. They went in with the protocol. They looked in all the places mice would be. They didn't find any.

Seth:
But in all three cases, they did find evidence of mice in the places where the victims worked. No major infestations, but droppings and traces. Enough.

Rachel:
So the public-health hypothesis on those two cases is that exposure happened at work, not at home.

Seth:
Which raises a different question. The county's public-facing guidance, for thirty-two years, has been about your own house. Seal up your woodpile. Don't sweep out the cabin without a mask. Don't shake out the blankets. Those are still good rules. But what if the more dangerous exposure is happening to people who clean other people's cabins for a living.

Rachel:
Short-term rental turnover is a multi-billion-dollar industry. In a town like Mammoth Lakes, almost every cabin you can rent is cleaned by someone whose job description does not say what to do if the previous renter left a mouse problem in the corner of the closet.

Seth:
There is actually a body of research on this exact question. After the twenty twelve Yosemite outbreak, an occupational-health review looked specifically at work-related hantavirus exposures. The cleaning staff at Curry Village were among the most heavily exposed. Some of them had been working in those signature tent cabins for years.

Rachel:
We are not going to name anyone. The Mono County Health Department has not released the names of the twenty twenty-five patients, and we are not going to push on that. The point is structural. The three twenty twenty-five cases together describe a different exposure profile than the historical pattern.

Seth:
And that profile points at people who work in the seasonal rental economy. Cleaners. Property managers. Maintenance workers. The people who open up a building that has been closed for two weeks and walk in first. One of the three twenty twenty-five victims was a twenty-six-year-old who worked at a Mammoth Lakes hotel.

Rachel:
If you clean cabins for a living, or you manage short-term rentals in a place like Mammoth Lakes, the relevant question is what kind of mask you wear on Saturday turnover.

Seth:
Federal cleanup guidance is specific. An N95 respirator is the minimum for indoor cleanup of the kind of space we have been describing. KN95 is the parallel certification standard. Cloth masks and surgical masks are not adequate for this kind of exposure.

Rachel:
We wear Armbrust KN95s on this show. Vector dot armbrust U S A... dot com. Thirty percent off anything Armbrust makes if you sign up for the newsletter.

Seth:
Back to the Mammoth Lakes story. And the part the town is having a hard time saying out loud.

Rachel:
Mammoth Lakes' economy is tourism. Skiing in winter, hiking and fishing and trail running in summer. The town's population is seven thousand but its visitor volume is in the millions. The local economy is the visitor economy.

Seth:
So when a deadly virus shows up in your town, the question you have to answer publicly is not just, what should we do about it. It is also, how do we communicate this without destroying the business that keeps the town alive.

Rachel:
This is a real tension. And to the credit of the Mono County health officials, they have been straightforward about it. By spring of twenty twenty-six the town was, on the surface, back to business. Underneath, it was more wary of this disease than it had been at any point in recent memory.

Seth:
A travel-forum thread that ran after the deaths were reported was titled, quote, "Be aware but don't panic." That is roughly the framing the local public-health messaging has tried to maintain.

Rachel:
You can imagine the calculus on both sides. If you under-communicate, you have a public-health problem. People keep cleaning cabins without masks, and you get more deaths. If you over-communicate, you have an economic problem. People cancel their bookings, and the seasonal workers whose exposure you are trying to prevent lose their jobs anyway.

Seth:
The town has been doing what we would call the careful version. Public statements. Pamphlets. Protocol updates for short-term rental operators. Mask recommendations for cleaning staff.

Rachel:
The criticism of that approach, mostly from public health voices outside the county, is that it is not enough.

Seth:
The defense of that approach, mostly from local officials, is that you cannot solve a workplace exposure problem by making your visitors panic. You solve it by making the workers safer.

Rachel:
Both of those things can be true.

Rachel:
Here is the question we kept coming back to while we were researching this episode. Why did the cases start in February.

Seth:
Hantavirus does not normally peak in February. It peaks in May, June, July. The deer mouse population is at its lowest in February, after the winter die-off. The viral load in any given mouse is lower because the mice are stressed and not breeding. The aerosolized exposure risk in any given enclosed space should be at its annual minimum in February.

Rachel:
And yet the first case of the year, in the worst hantavirus county in California, happened in February.

Seth:
There are a few possibilities. One. It is a coincidence of timing. Three unrelated exposures that happened to overlap. Two. The mouse population in the Sierra has been behaving differently. Deer mouse numbers are high this year in Mammoth, and probably elsewhere in the Eastern Sierra. The winter has been milder. The mice are not dying off the way they used to. The viral load is staying high through the off-season.

Rachel:
And here is where the precedent matters. The original nineteen ninety three Four Corners outbreak was preceded by a twenty-fold increase in the deer mouse population, driven by the nineteen ninety-two through ninety-three El Niño event. The same climate dynamic that started this disease's American history may be starting another chapter.

Seth:
Three. The exposure environments have changed. There are more short-term rentals being cleaned in February than there used to be, because the Sierra ski season has been getting more weather-volatile. A storm closes the resort for a week. The cabin sits empty. Then it's a busy weekend and twelve cleaners spend Saturday going in and out.

Rachel:
We are not going to pretend we know which of those is the right answer. The Mono County Health Department is investigating, and the CDC has been notified. Hantavirus pulmonary syndrome has been a nationally notifiable disease since nineteen ninety five, which means there is a paper trail.

Seth:
But the timing is the part that the ecologists we talked to are most interested in. Because if the answer is the second one, that the mouse populations themselves have been changing, that is a much bigger story than three deaths in a small town. Recent climate modeling suggests hantavirus-carrying rodents will expand their range with continued warming.

Rachel:
Either way, this is a question that is going to keep coming up.

Rachel:
The three Mammoth Lakes patients have not been named publicly. Their families have asked for privacy, and the county has honored that. There is something quietly important about that, in a country where every other notable death becomes a national news story within forty-eight hours.

Two weeks after the third Mammoth Lakes death, in a different state, a different person came down with the same disease and died of it. Her husband was Gene Hackman. He died eight days later, alone in the house with her body.

Some people online are already trying to draw a line between these. Three deaths in a small ski town. A famous death in Santa Fe. A disease that, until last year, almost nobody in this country had heard of.

We are going to be careful about what that means.

That is episode three.

Seth:
I'm Seth Avery. Vector publishes new podcasts each week as the story develops. Subscribe so that you don't miss important updates.

Rachel:
And I'm Rachel Marin. If you work in or near the kind of building this episode was about, go to vector dot armbrust U S A... dot com, sign up for the newsletter, and get thirty percent off anything Armbrust makes.

Seth:
Vector is a Vector Media production for Armbrust USA. The information in this episode is journalism, not medical advice. If you think you may have been exposed to hantavirus, contact your local public health department or a medical provider. We are not a substitute for either.