Why do hundreds of Grand Canyon tourists suddenly get sick?

While hiking in the Grand Canyon National Park, Kristi Key came across a worrying place: four hikers resting on the side of the trail, and looking a little worse for wear. After learning that two of the hikers had spent the previous night throwing up violently, Key offered to call a rescue team, but the group refused. But when she saw them sitting in the same place on the way home, with one of the hikers still vomiting, she knew it was time to call for help.

Finally, a helicopter appeared, which flew the nauseous man to safety. But the experience stuck with Key, who told The Daily Beast that she has hiked hundreds of miles in the Grand Canyon and never come across hikers whose illness was not related to dehydration or heat until now. After a once healthy member of the unfortunate group fell ill later that day, Key began to suspect that a virus was to blame.

Key is not alone in the history of nausea, as the Grand Canyon National Park is currently experiencing an outbreak of a gastrointestinal disease very similar to norovirus, a disease that can cause vomiting, diarrhea, cramps, body aches and mild fever. According to the CDC, norovirus is “highly contagious” and anyone can become infected – the disease can be spread through direct contact with an infected person, contact with a contaminated surface or ingestion of contaminated food or drink. While the symptoms can be very unpleasant, norovirus rarely leads to death or serious illness.

As of June 10, the park knew of 118 people who have become ill from a gastrointestinal virus, which was reported by the Grand Canyon News. The infections have spread over 16 different trips on the Colorado River and in the hinterland.

A majority of the diseases were registered in May, and the last case was reported on 2 June. According to Jan Balsom, head of communications, partnerships and external affairs at the office of the Superintendent of Grand Canyon National Park, the park has been issuing alerts about gastrointestinal viruses since May 20.

“We have not seen such an outbreak in about 10 years,” Balsom said. In fact, Balsom herself had an inlet with what she called the “unusual” spread of gastrointestinal problems when a woman on a river trip she recently participated in contracted a stomach virus less than 12 hours into the journey. However, the woman does not know if she was infected with norovirus or another disease, a situation that illustrates many of the difficulties in investigating the outbreak.

There is a limited amount of time where one can collect stool samples to confirm a norovirus infection, Balsom said. River trips usually last longer than the critical window, which means that it is often impossible to accurately diagnose a person’s disease.

The park asks visitors to make sure that their water is not just filtered, since norovirus is not killed by filters for on-site use. It must be either chemically disinfected or boiled. It also asks that visitors not drink from waterfalls, pools or streams.

A public health team composed of a number of state and federal offices is investigating the outbreak. Balsom explained that the Colorado River and the hinterland are non-contiguous areas, which contributes to the mystery of the cases.

“[Officials] has followed up with interviews from participants from trips that have become ill, Balsom said. “They have tested aft deck scans to try to find out if it is noro or not.”

In a statement to The Daily Beast, an official at the National Park Service Office of Public Health described the outbreak as an “enhanced GI disease” and said an investigation would “assess all potential sources. It is currently unknown what the source of the disease is.”

Individuals have taken to social media to share their stories of trips that have been cut short by vomiting, and have posted long sagas about hikes that have gone horribly wrong.

A man wrote about being overwhelmed by vomiting in the middle of the night, with nausea attacks that lasted from kl. 01.00 to 05.00

“Let me tell you,” he wrote, “being sick and weak and walking 1200 feet at an altitude of 1.5 miles is no movement.”

In another post in May in the “Grand Canyon Hikers” Facebook group, a woman warned others about the norovirus outbreak and described that she became ill shortly after leaving the canyon.

“I could not have gone out or taken care of myself if I had started throwing up in the canyon,” she wrote. “GC’s public health officials are tracking the situation. It’s obviously a big one. “