MISSOULA — Missoula's Community Medical Center has only seen one case of norovirus so far this winter but cautions that with outbreaks across the country, it's increasingly important to know the symptoms.

The U.S. Centers for Disease Control and Prevention (CDC) notes norovirus is a very infectious gastrointestinal virus and is also the leading cause of foodborne illness in the U.S.

• RELATED: CDC data shows surge in norovirus cases in parts of the US

Many cases resolve on their own without being tested or treated by doctors, which means it's almost impossible to know how many people are sick. But recent figures show rates of positive norovirus tests have reached the highest weekly levels on record in years.
Symptoms present as vomiting and diarrhea but norovirus is different than the stomach bug or flu since they have different viral origins.

While anyone can get Norovirus, there are a few populations that are more susceptible than others.

"Adults that are over 65 years of age, very young children, [the] pregnant population, they have to be extra careful. Come to the hospital if they feel weak, tired, fatigued, and have severe symptoms," CMC's Nitin Sainani told MTN.

The CDC reports you can still spread norovirus for up to two weeks after being sick even if you feel better.