Over the past two months, roughly two dozen people have fallen ill with flu-like symptoms following river rafting trips through Grand Canyon National Park. Symptoms have been severe enough in some instances to require hospitalization, and public health officials have so far been unable to identify a cause.

Outbreaks of illness on the Colorado River are not unheard of, although they remain rare. Most recently, in 2022, more than 200 rafters and backpackers contracted norovirus, a highly contagious virus that causes acute gastroenteritis. Even less common, though, is for the cause of an outbreak to baffle medical experts.

The first cases in the recent outbreak appear to be linked to private rafting trips that traveled the Lee’s Ferry to Diamond Creek corridor of the Colorado River between May 18 and June 22. Four of the 16 members of one expedition reported symptoms within a week or two of returning home, including fever, chills, fatigue, weakness, and joint and muscle soreness progressing to severe pain. Several people later sought treatment for a buildup of fluid in their lungs, and at last one developed a raised rash and bruising on their shin that felt similar to a broken bone.

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At least two people experienced symptoms severe enough to require hospitalization, including one who lost consciousness while in the doctor’s office, according to one member of the group, who posted about his experience on Facebook.

Matthew Wappett, the executive director of the Institute for Disability Research, Policy & Practice at Utah State University, was one of those people. An experienced rafter who was rafting the Grand Canyon for the first time, Wappett became ill shortly after returning home from a 16-day trip that ran May 18 to June 2. It began, he told SFGATE, with a painful swelling in his knee that quickly spread into a full-body ache and fever. By June 7, he was in the hospital. 

Matthew Wappett, an experienced rafter who was rafting the Grand Canyon for the first time, became ill shortly after returning home from a 16-day trip, which ended up with him in the hospital.

“It’s been a surreal experience to have to go through something like this, where you don’t even know what’s wrong with you,” Wappett said, adding that now, weeks later, he continues to struggle with pain, weakness and general malaise. His family recently left for another rafting trip on the Salmon River, but Wappett chose to stay home.........

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