Over 200 rafters, backpackers affected by norovirus in Grand Canyon

PHEONIX — More than 200 people who visited the Grand Canyon National Park over the spring contracted norovirus, federal health officials said.

At least 222 people who participated in a river rafting trip or backcountry backpacking between April 1 and June 17 contracted the illness, which led to symptoms of vomiting, diarrhea and nausea, according to a Centers for Disease Control report.

Most of the cases were seen in park visitors, impacting 191 people, while the rest of the cases were seen among professional guides, affecting 31 people.

It was concluded that pooled portable toilets from nine affected trips were tested positive for norovirus.

After dozens of cases were brought to the park’s attention, on May 24, the National Park Service requested the CDC get involved and an investigation was launched.

The norovirus-associated acute gastroenteritis is highly transmissible in areas with close person-to-person contact where there is limited access to hand hygiene, like backpacking or rafting.

The first reported case of the illness on April 8 came from a commercially operated rafting group that said at least seven people had been experiencing vomiting or diarrhea. Nine additional trips in the coming weeks saw 102 cases of acute gastroenteritis documented.

As it stands, commercial guides are required to report illnesses at each trip’s end while also completing an illness report form for each person, while private rafting trip guides are required to report illness no more than seven days after finishing the trip. Backpackers are not required to report illness but are otherwise encouraged.

Park visitors were contacted by email and some submitted surveys of their experience and symptoms in the Grand Canyon or in the days following.

Since the outbreak, control measures were implemented, including rapid case reporting, symptom screening before the trip begins, water disinfection and minimizing interactions among rafting groups.

Other recommendations included the regular disinfection of portable water spigots throughout the backcountry and advertisement of proper handwashing with soap and water whenever possible. The report noted that many staff members said they weren’t aware that alcohol-based hand sanitizer is ineffective in protecting against norovirus transmission.

Experts added that pooled portable toilets from two unaffected trips tested negative for norovirus. The toilets were not tested for other pathogens.

In total, people from 34 states and four countries contracted the illness.

More analysis is underway to examine an epidemiologic overlap among the ill, and rafters and backpackers who were not affected.

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