About 30 Yellowstone National Park employees were infected with norovirus this week and last, according to park spokesman Al Nash.
The outbreak happened in Mammoth Hot Springs. It was believed to have come to the park through several tourists suffering from gastrointestinal problems, according to AP.
Infected employees, after their symptoms appeared, were isolated for several days to prevent further infection. Public spaces were also cleaned more rigorously in the wake of the outbreak.
There is no treatment for norovius, which results from contact with vomit, stool or someone else with norovirus. Symptoms include nausea, diarrhea and abdominal pains. Rest and hydration are recommended.
The Yellowstone norovirus outbreak peaked last weekend and is on the decline now.