In the 2012 summer season, recurrent outbreaks of norovirus occurred among different rafting groups on the Colorado River in the Grand Canyon National Park. Confidential illness reports were completed by individuals with symptoms of acute gastrointestinal illness. Samples of fecal matter, vomitus, surface swabs of rafting equipment and environmental swabs at stops along the hiking corridor were collected and tested for norovirus.

Between May 9 and July 9, 2012, 97 rafters from 10 trips experienced gastrointestinal illnesses. Investigators concluded that norovirus was likely introduced by ill or asymptomatic individuals actively shedding the virus in their vomitus or feces, and spread within, or between, river trips by different modes of transmission.