In May 2022 the National Park Service Office of Public Health and the Coconino County Health and Human Services Department notified the CDC of an outbreak of acute gastroenteritis cases among backcountry visitors to the Gran Canyon National Park. The agencies reviewed illness report forms, assessed infection prevention and control (IPC) practices, and distributed a detailed survey to river rafters and hikers with backcountry permits (backpackers) who visited the Grand Canyon backcountry. During April 1–June 17, a total of 191 rafters and 31 backpackers reported symptoms consistent with acute gastroenteritis. Specimens from portable toilets used by nine river rafting trip groups were tested using real-time reverse transcription–polymerase chain reaction and test results were positive for norovirus.

Ill visitors were from 34 U.S. states and four additional countries.