Adam Kramer, a public-health specialist for the National Park Service, says the gastrointestinal illness affected tourists on twelve separate trips with five tour companies, all Utah-based.
Kramer says a stool sample tested positive for norovirus, the family of common viruses known to cause illness among many cruise ship passengers. Norovirus can cause intestinal distress that typically lasts from one to two days.
Most of the victims seem to have gotten sick at the start of the trips; one person had to be airlifted from the canyon due to complications.
The trips usually last up to two weeks if participants follow the full 200-mile route from Lee's Ferry to Lake Mead.
Barbara Worgess, Coconino County health services director, says the investigation is focusing on meat products in warehouses owned by the river-tour companies.
