Norovirus in the Desert? How the Outbreak Spread Along the Pacific Crest Trail

In September of last year, Kevin Quinn was traveling in a remote mountainous region in central Washington state when he began to feel unwell. "At first, I thought it was just stomach pain," he says, "but when we reached the camp, I started vomiting, and the vomiting continued to the other end."

He was hiking north along the Pacific Crest Trail, a 2,600-mile, five-month trek from the Mexican border to Canada that has gained popularity over the past decade, thanks in part to Cheryl Strayed's memoir "Wild," which was adapted into a movie in 2014.

Quinn was hiking the trail with his daughter, who had taken time off work to embark on the journey together. After several months on the trail, he found himself debilitated at a campsite in the middle of the desert.

"I had heard about norovirus for many 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 it when you're out on the Pacific Crest Trail."

Norovirus is a highly contagious virus that can cause severe gastrointestinal illness lasting several days. It's often associated with closed, crowded spaces such as cruise ships, healthcare facilities, and childcare centers.

But it can also emerge in the wilderness, as it did last year during an outbreak among hikers like Quinn, which was documented in a recent investigation by the Centers for Disease Control and Prevention (CDC).

Calling in Disease Detectives

After a stream of sick hikers passed through the Washington Alpine Club's Snoqualmie Pass lodge last summer, volunteer Robert Henry closed down the hostel-style accommodations and sent an email to health authorities.

"At that time, my concern was to make sure that the hikers on the trail didn't get worse and that the Washington Alpine Club volunteers didn't get exposed to what they were bringing in," Henry says. He also worked to alert other hikers to the threat.

One of Henry's warning messages reached Arran Hamlet, an epidemiologist with the CDC's Epidemic Intelligence Service (EIS) based in the Washington State Department of Health. When Hamlet learned of the outbreak, he conducted a survey for the hikers to fill out. He heard from approximately two dozen hikers who reported gastrointestinal symptoms, and he says social media posts suggested there were many more.

Hamlet focused on a 70-mile stretch of the trail south of the lodge where the sick hikers had passed through. He learned that one common stopping point for rest was a remote log cabin in a meadow with an outhouse and a stream used for drinking water.

Hamlet and his team visited the cabin and tested the water from the stream. They also swabbed toilets, door handles, countertops, poker chips—anything that people might have touched. While the water samples turned out to be clean, "every [surface] swab came back positive for fecal contamination," he says.

"That doesn't mean we can see human feces on things," he adds, "but at some point, there was a transfer of fecal contamination to every surface in the cabin we swabbed, as well as throughout the restroom."

The findings 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 spread among hikers and that "the impact of contaminated surfaces inside the cabin and... restrooms likely amplified transmission."

Surface transmission is one of the simple ways diseases can spread among hikers: an infected person can contaminate their hands or clothing during defecation or vomiting. They can then spread the virus to shared surfaces touched by other hikers, such as restroom door handles or communal camping equipment. These hikers could touch their mouths, ingest viral particles, and become ill. They can also become infected by consuming contaminated food or drinking water.