Thru-Hikers’ Worst Enemy Is Microscopic: Why Norovirus Is a Perennial Problem on Trails

When most of us imagine things that could go wrong on a thru-hike, we probably think of ankle and knee injuries, getting lost, bad weather, and equipment failure. And yet, in huts and trail bathrooms, a far worse threat lingers, and it’s one we can’t even see: norovirus.

A recent outbreak on the Pacific Crest Trail (PCT) left over 20 hikers seriously ill — and that’s not uncommon. Each year, multiple hikers on the PCT and Appalachian Trail (AT) get sick with this highly contagious illness, and it’s serious enough to end a thru-hike attempt. There’s a reason it thrives in the backcountry, and a few strategies you can use to stay safe.

What Is Norovirus?

Although it’s often called the stomach flu, norovirus is a separate illness that’s distinct from the influenza virus. The main symptoms are diarrhea, vomiting, nausea, stomach pain, fever, headache, and body aches, according to the Centers for Disease Control (CDC). It can quickly lead to dehydration. Symptoms usually appear within 12 to 48 hours of exposure, and people can remain contagious for up to 2 weeks.

Norovirus is extremely contagious. People can catch it by direct contact with an infected person or by touching a surface that has been touched by an infected person. The virus can survive on surfaces for weeks. Norovirus can also contaminate water supplies.

“You can get norovirus by accidentally getting tiny particles of feces (poop) or vomit in your mouth from a person infected with norovirus. If you get norovirus illness, you can shed billions of norovirus particles that you can’t see without a microscope,” the CDC explains on its website. “It only takes a few norovirus particles to make you and other people sick.”

Given its high contagiousness, norovirus is often a problem in confined spaces like cruise ships. There have been two major outbreaks on cruise ships this year so far. It’s also a problem in food service. If someone preparing food is sick and doesn’t wash their hands, it can easily infect someone who then eats the prepared meal.

Why Is It a Problem on Trails?

The main defense against norovirus is thorough hand washing with soap and water. Hand sanitizer does not effectively work against the virus. Of course, on the trail, access to soap and water is limited. Hikers are far more likely to use hand sanitizer after using the bathroom.

If someone is infected and uses a trail latrine or touches a shared surface in a shelter, those spaces in the middle of nowhere aren’t likely to be cleaned with bleach any time soon. That means the virus can linger on those surfaces for weeks.

On hikes and river rafting trips, “handwashing and clean water supplies can be limited. These factors, along with people sharing small spaces, can lead to quicker spread of norovirus among people on the trip,” the CDC explains.

Thru-hikers often have to use whatever water source they can find. Most water filters don’t remove norovirus. Boiling water is an effective way to kill viruses, and water purifiers, like the Katadyn Explorer Pro, also remove them from water sources. Most thru-hikers aren’t going to boil all their water if they’ve used a filter. That means that a single contaminated water source can quickly infect a large group.

Recent Norovirus Cases

A current outbreak on the PCT is likely due to a bad water source. Approximately two dozen hikers became ill after drinking from a water cache at Swarthout Canyon in Southern California. The Pacific Crest Trail Association did not confirm that the water cache was the source, but it did confirm that it is working with officials from the San Bernardino County Department of Public Health and U.S. Forest Service, as well as local land managers, to address the outbreak.

A CDC report on an outbreak that affected 27 people on the PCT in Washington state in 2022 explained that exposure to contaminated surfaces in a cabin and latrines “likely amplified transmission.”

The Appalachian Trail Conservancy (ATC) reports receiving news of at least one outbreak per year. GJ spoke with an ATC representative, who explained that, so far in 2026, 30 people have had a stomach bug on the AT. These were not confirmed norovirus cases. However, this data point suggests that gastrointestinal illnesses can occur.

In 2022, 222 people from multiple river-rafting trips in the Grand Canyon became ill with norovirus. On each trip, up to 83% of participants became infected.

Prevention Strategies

Whenever possible, wash your hands thoroughly while on trail before preparing food and after using the bathroom. Be sure to keep your cooking/dining and sleeping areas at least 200 feet away from any bathroom/place with human waste.

The CDC also recommends using bleach wipes when possible to disinfect shared surfaces. Do not share food, water, or utensils with other hikers.

If you are in an area with an outbreak, avoid shared spaces and bathrooms. Ill hikers should isolate themselves from healthy individuals. If you hear news of an outbreak nearby, be sure to boil all water for at least 1 minute (or 3 minutes if above 6,500 feet).