The Department of Public Health and Human Services says norovirus is on the rise in Montana.

"Currently, we know that almost 300 individuals became ill as part of outbreaks that were reported to us, but we also know that there are a large number of individuals that never get tested or report, so the number of people [with norovirus] is likely much higher," said Foodborne Epidemiologist Dana Fejes.

The main symptoms include diarrhea and violent vomiting. Most people who get the virus recover within 1 to 3 days, but it dangerous to those with weak immune systems, the young and the elderly.

"The main thing that will help prevent norovirus infection is to wash your hands frequently with soap and water, and to stay home when you are sick with norovirus so you prevent spreading the virus in the community," Fejes said. "Another thing you can do is to try not to prepare food for others while you are sick with vomiting and diarrhea."

Norovirus is always in the population, but typically spikes in winter and begins to decline after January.