Last September, Kevin Quinn was trekking through a remote, mountainous region in central Washington state, when he started feeling sick. "At first, I thought it was just a stomachache," he says, "But when we got to the campsite I started throwing up, and it started coming out the other end as well."

He was hiking north on the Pacific Crest Trail – a five-month, 2600–mile trek from the Mexican border up to Canada that's gotten popular in the last ten years thanks to the memoir Wild, by Cheryl Strayed, which became a movie in 2014.

Quinn was on the trail with his daughter, who had left her job so they could hike together. After months of hiking, he found himself wiped out at a campsite in the middle of nowhere.

"I had heard about the norovirus for years, but it was always in the context of 'Oh, there's a cruise ship in the Caribbean,'" he says, "You don't think about this being an issue when you're out on the Pacific Crest Trail."

Norovirus is a highly contagious virus that can cause serious gastrointestinal distress for several days. It's often associated with enclosed, crowded settings like cruise ships, health care facilities and childcare centers.

But it also crops up in the wilderness – like in an outbreak among hikers like Quinn last year which was documented in a recent investigation by the Centers for Disease Control and Prevention.

Call in the disease detectives

After a stream of sick Pacific Crest Trail hikers came through the Washington Alpine Club Lodge near Snoqualmie Pass last summer, a volunteer named Robert Henry closed the dorm-style lodge and emailed health authorities.

"My concern at the time was to make sure that the hikers on the trail didn't get any worse, and to make sure that the volunteers at the Washington Alpine Club didn't contract whatever it was they were bringing in," Henry ways. He also worked to warn other hikers about the threat.

One of Henry's alert messages reached Arran Hamlet, a disease detective with the CDC's Epidemic Intelligence Service, based at the Washington State Department of Health. When Hamlet heard about the outbreak, he made a survey for hikers to fill out. He heard from some two dozen hikers who experienced symptoms of gastrointestinal illness – and says social media reports indicate there were many more.

Hamlet focused on a 70-mile stretch of trail south of the Lodge, where ill hikers were coming from. One common rest stop, he learned, was a remote log cabin in the meadows, with a pit latrine and a stream that's used for drinking water.

Hamlet and his team hiked out to the cabin and tested water from the stream. They also swabbed the toilets, the door handles, the tabletops, the poker chips – anything people were touching. While the water samples came back clean, "every single [surface] swab tested positive for fecal contamination," he says.

"This doesn't mean that we can see human feces on things," he adds, "but at some point in time, there was transmission of human fecal contamination onto every surface in the cabin we swabbed, and also everywhere in the latrine."

The results of the investigation were published this month in the CDC's Morbidity and Mortality Weekly Report. Investigators concluded that there was an outbreak of norovirus on the trail last summer that was spreading between hikers and that "exposure to contaminated surfaces within the cabin and ... latrines likely amplified transmission."

Surface transmission is one easy way the disease could spread among hikers: Someone who is infected could contaminate their hands or clothing when they defecate or vomit. They may spread the virus onto shared surfaces that other hikers touch, such as a latrine door handle, or a shared utensil at the campsite. Those hikers could touch their mouths, ingesting virus particles and becoming sick. They could also get it from eating food or drinking water that's been contaminated.

Shanna Miko, a nurse epidemiologist at CDC, was part of the field team on the Pacific Crest Trail study — and it wasn't her first norovirus-in-the-woods investigation. Last year, she traced an outbreak at the Grand Canyon, among people who were backcountry hiking and whitewater rafting.

"These are very well-planned trips. For many people, they're once-in-a-lifetime," she says. Travelers often read books and blogs in preparation, and get advice from others who have done the trip before them, accumulating trail wisdom – "places where people frequently stop, or places that have shelters where people frequently sleep over," good places to get water, or use the bathroom, she says.

These hubs, which seem so remote, see thousands of people – in varying levels of wellness – pass through in a season. They may not leave visible traces but some may leave germs, like norovirus, that can live on environmental surfaces for a long time, Miko says. (According to the CDC, this hardy virus can stay alive on surfaces for "days or weeks.")

Hand sanitizer doesn't cut and other advice for staying well

With norovirus, hand sanitizer and common water filters don't work. The virus is small, and "extra sticky" on skin, Miko says. And it takes just a few dozen viral particles to make a person very ill.

Miko says there are ways that hikers can cut their risks.

Always wash your hands with soap and water after you have a bowel movement – and wash them again before you eat. "The soap is a great detergent to remove the virus from your hands," she says. While any soap and water will work, she recommends biodegradable soaps in protected national parks and backcountry woods to reduce the impact on the environment.

Make sure to drink and cook with good, clean water. Pay attention to where the water comes from, and treat it properly. "Boiling for at least three minutes is the best way to kill everything you would typically come across," Miko says. And note: Most water filters are good at removing bacteria and common parasites but they don't cut it when it comes to norovirus. You'll need to layer on either chemical treatment or UV light treatment to kill the virus. (Here's the CDC's breakdown of what works for which pathogens.)

If you do fall ill, shelter in place if you can. This is for your own safety, and for the sake of others, "so you aren't seeding norovirus particles along the trail and putting others at risk," Miko says. This is not the time to try to push ahead but to rest and hydrate. "If possible, try to keep your defecation far from the trail and bury it, and don't prepare food anywhere near where you're using the restroom or vomiting," she says.

The worst of the symptoms usually passes in two to three days, though "you can still spread norovirus after you feel better," Miko says. She recommends waiting at least two days after symptoms have resolved before continuing on.

Norovirus was the last straw

Kevin Quinn thinks he got norovirus because he broke his own rule. "We were told not to drink from standing water, and I did the one time," he says. It was a dry year, and the streams in the section he was hiking had run out.

He was thirsty, he was really tired – and while he filtered the water, he skipped the additional, chemical treatment. Soon, he knew he'd made a mistake. "I was completely debilitated. I didn't have the energy to set my tent up," he recalls, "All I was doing was, like, every 15 minutes, going off into the woods and either throwing up or having diarrhea."

After a night of being very ill, Quinn and his daughter made a long, slow trek out of the woods. "We never made the whole trail," he says, "We just decided to call it quits."

Earlier in the summer, he caught COVID, which derailed his trail plans for a month. Up ahead, there were wildfires and trail closures. For Quinn, getting norovirus was the last straw.

A year later, he still regrets that he didn't take the time to treat the water properly.

To other hikers – he says: heed the signs, wash your hands and make sure your water is clean. In his experience, it's not worth the risk.

The story was edited for web by Carmel Wroth and for air by Scott Hensley.