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

Minnesota health officials are warning of an increase in norovirus cases amidst holiday gatherings. The Minnesota Department of Health on Monday said over 40 outbreaks of the stomach virus have been reported this month, which is almost twice the usual number.

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