Minnesota health officials are warning of an outbreak of a highly contagious illness: norovirus. The Minnesota Department of Health is reporting 40 outbreaks of norovirus, otherwise known as the stomach flu.

The department defines an outbreak as an incident in which two or more persons experience a similar illness after a common exposure.

The has received more than 40 reports of norovirus outbreaks so far this December, almost twice the usual number. The department as an incident in which two or more persons experience a similar illness after a common exposure.

The Minnesota Department of Health says there have been more than 40 reported norovirus outbreaks this December, nearly double the usual number. Norovirus, also known as the stomach flu, is highly contagious and causes vomiting and diarrhea.