Norovirus may be to blame for 2022 Pacific Crest Trail hiker gastroenteritis outbreak

Key points:

• A CDC investigation found 27 reports of acute gastroenteritis among Pacific Crest Trail hikers.
• Many people report a shorter duration of illness, with symptoms such as fatigue, vomiting and diarrhea.

An outbreak of acute gastroenteritis among hikers on the Pacific Crest Trail in Washington state in late summer 2022 was likely caused by norovirus, according to a CDC investigation. Morbidity and mortality weekly reports.

Previously, between April and June 2022, the largest outbreak of acute gastroenteritis (AGE) on record occurred in a remote area of ​​Grand Canyon National Park, affecting at least 222 backpackers and rafters. Preliminary data at the time suggested norovirus was the cause.

“On August 26, 2022, the Washington State Department of Health received informal reports of numerous Pacific Crest Trail hikers suffering from AGEs,” Dr. Alan Hamlet, wrote an Epidemic Intelligence Service official and colleagues at the Centers for Disease Control and Prevention (CDC). “An investigation of a Sept. 5 social media post found 27 AGE reports submitted by Washington’s Pacific Crest Trail hikers in the last month, 26 of whom provided information on the date of symptom onset.”

Investigators conducted a REDCap survey, which was posted to a Facebook group for Washington Pacific Crest Trail hikers and accessible via a QR code at trailheads where illnesses were reported. They collected responses from 27 people who reported AGE symptoms, 22 of whom also reported the date of onset. Two respondents who had developed symptoms within the past 14 days provided stool samples that tested positive for norovirus.

Twenty people (74%) reported short-term illness (median = 2.5 days; 95% CI, 1-15.7), with fatigue most commonly reported among the 22 symptomatic respondents (81%) (95 %), followed by fatigue (95%). Vomiting and diarrhea (77%). In addition, 21 people reported becoming ill within 73 miles of the Washington Crest Trail “suggest the possibility of environmental exposure,” investigators wrote.

Analysis of drinking water samples collected in early October did not detect norovirus, fecal culture-based indicators, E. coli or human-specific fecal contamination; however, swabs collected from high-touch surfaces in huts and toilets did test positive for human-specific fecal contamination.

Although investigators were unable to detect norovirus through environmental sampling, they determined that the outbreak was caused by norovirus and was likely spread through contact with contaminated surfaces.

“Norovirus prevention in remote areas is difficult because of the lack of easy access to clean water and hand soap, and the inability to routinely disinfect shared surfaces,” Hamlet and colleagues concluded. “In addition, alcohol-based hand sanitizers commonly used during hiking Not effective against norovirus.”

They continue, “Preventing future outbreaks requires raising awareness of the importance of handwashing and the lack of effectiveness of alcohol-based hand sanitizers against norovirus, and more frequent cleaning of public facilities; social media monitoring may help Detect epidemics early.”