MISSOULA, Mont. -

A gastrointestinal outbreak in Ravalli County forced a Hamilton nursing home to shut its doors to outside visitors to prevent the spread of Norovirus.

Ravalli County Public Health Director Judy Griffith said the first case of the virus was reported at Valley View Estates Nursing Home November 24. Since then it's ballooned to at least 50 cases.

"A combination of residents and staff at Valley View report symptoms of nausea, vomiting and diarrhea," said Griffith. “

Norovirus is better known as the stomach flu, but it can still be dangerous. Griffith said seniors are one of the groups most at risk.

"A lot of times, it is the elderly. We have such a fragile population in the elderly when they become dehydrated,” said Griffith. “They're in a compromised state to begin with, so it's harder for them to recuperate,   

Griffith said public health investigators found the nursing home to be in compliance with health and sanitation standards, which indicates the virus was spread from someone outside.

Children are another at risk group for contracting Norovirus. Griffith said a simple practice like washing your hands regularly can help halt the spread of infection.

"Hand washing - an old fashioned thing called hand washing - is really important. Stay home if you're sick. If you've got children that were sick, keep them home, and once you become well, you need to stay home for at least three days. If it’s viral, you could still be shedding the virus.”

Griffith said recovery for some of the people infected has already started.

"Right at this point, people that were sick earlier in the week or last Saturday are already getting well."