Norovirus likely culprit of 2022 gastroenteritis outbreak among Pacific Crest Trail hikers
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Key takeaways:
- A CDC investigation identified 27 reports of acute gastroenteritis among Pacific Crest Trail hikers.
- Many reported an illness of short duration, with symptoms of fatigue, vomiting and diarrhea.
An acute gastroenteritis outbreak in late summer 2022 among hikers on the Pacific Crest Trail in Washington was likely caused by norovirus, according to a CDC investigation in Morbidity and Mortality Weekly Report.
This followed the largest outbreak of acute gastroenteritis (AGE) recorded in the Grand Canyon National Park backcountry, which occurred from April to June 2022 and affected at least 222 backpackers and rafters. Preliminary data at that time suggested norovirus was the cause of illness.
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“On August 26, 2022, the Washington State Department of Health received informal reports of numerous Pacific Crest Trail hikers with AGE,” Arran Hamlet, PhD, an epidemic intelligence service officer at the CDC, and colleagues wrote. “An investigation of social media postings on September 5 found 27 reports of AGE by Washington Pacific Crest Trail hikers during the previous month, 26 of whom provided information about symptom onset date.”
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 trailhead locations with reported illness. They collected responses from 27 individuals who reported symptoms of AGE, of whom 22 also reported onset dates. Two respondents with symptoms in the previous 14 days provided stool samples, which tested positive for norovirus.
Twenty individuals (74%) reported an illness of short duration (median = 2.5 days; 95% CI, 1-15.7) and, among 22 respondents (81%) with symptoms, the most commonly reported was fatigue (95%), followed by vomiting and diarrhea (77%). In addition, 21 individuals reported becoming ill within a 73-mile stretch of the Washington Crest Trail, which “suggested the potential for environmental exposure,” investigators wrote.
Analysis of drinking water samples collected in early October did not detect norovirus, culture-based fecal indicators, Escherichia coli or human-specific fecal contamination; however, swabs collected from high-touch surfaces in cabins and latrines did test positive for human-specific fecal contamination.
Although investigators were unable to detect norovirus via environmental sampling, they determined the outbreak was caused by norovirus, likely spread by contact with contaminated surfaces.
“Norovirus prevention in remote areas is difficult because of a lack of easily available clean water and soap for handwashing, and inability to routinely disinfect shared surfaces,” Hamlet and colleagues concluded. “Moreover, alcohol-based hand sanitizers, commonly used in hiking, are not effective against norovirus.”
They continued, “Preventing future outbreaks will require fostering increased awareness of the importance of handwashing and lack of effectiveness of alcohol-based hand sanitizers against norovirus, and more frequent cleaning of public facilities; early outbreak detection might be facilitated by social media surveillance.”
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