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It’s thru-hiking season on America’s long trails—and, once again, that means it’s norovirus season, too.
On Wednesday, Shenandoah National Park officials issued a notice that they had received several reports of severe sickness along the Appalachian Trail (AT). The park service suspects norovirus, a highly contagious illness that can cause nausea, vomiting, and diarrhea.
While norovirus is most active between November and April and thrives in enclosed environments like cruise ships, it isn’t uncommon for the virus to make a summertime appearance in popular outdoor spaces like the Appalachian Trail. In fact, the Appalachian Trail has seen suspected Norovirus outbreaks on several occasions over the past several years. Last spring, the National Park Service issued warnings in North Carolina, Georgia, and Tennessee after hikers began experiencing gastrointestinal symptoms. In 2022, other popular outdoor destinations like a 70-mile section of the Pacific Crest Trail (PCT) saw outbreaks; that same year, the biggest outbreak in the Grand Canyon’s history took place after 222 rafters and backpackers reported the illness. And in 2024, Hawaii closed the entire Kalalau Trail due to the virus.
The virus is generally transmitted through fecal matter, and due to its structure, it’s resistant to the alcohol-based hand sanitizers that thru-hikers often use on long trails. An investigation into the PCT outbreak found that the water sources at one particular rest stop were clean, but that nearly every surrounding surface tested positive for fecal matter.
Every year, norovirus breaks out about 2,500 times across the United States, causing severe distress for one to three days. It can remain contagious for two days after symptoms dissipate, which can create challenges for thru-hikers who are unable to quarantine for a week.
Transmission of the virus requires just a few dozen virus particles although less exposure to the virus generally results in mild symptoms. Outbreaks are most likely to occur in situations where food is and water is being shared, or surfaces are contaminated like privy door handles, and shared utensils.
Up until February of this year, Moderna was conducting a late stage trial of an mRNA vaccine for norovirus when the FDA placed it on hold after a single subject developed Guillain-Barré Syndrome. Some research has even suggested that an individual’s blood type can determine how likely they are to contract norovirus, with those with type B blood showing resistance to the virus while those with A, AB, and O blood types have a tendency towards contracting it.
The best way for at-risk individuals to avoid getting sick? Hygiene. Hikers should wash their hands regularly with soap and water for 20 seconds, properly dispose of human waste by packing it out or avoiding water sources by 200 feet, and disinfecting water (keeping in mind that the most popular filters along the Appalachian Trail are unable to remove viral pathogens, requiring additional boiling or alternative treatment methods).
While traveling through popular parts of the Appalachian Trail like Shenandoah National Park, hikers might also avoid shelters and regularly use soap, which they can often find at the park’s waysides.
The Appalachian Trail Conservancy encourages hikers who suspect they’ve contracted norovirus to report their cases to stomachbug@appalachiantrail.org.
From 2025