State health officials have confirmed the cause of an illness that struck patrons of a southwest Kansas restaurant last month.

The Kansas Department of Health and Environment said Monday the gastrointestinal upset among people who ate food from a Jimmy John’s Gourmet Sandwiches in Garden City was caused by norovirus.

County and state agencies began investigating the outbreak Dec. 18. 

KDHE says it found that 209 people came down with norovirus symptoms such as vomiting and diarrhea within three days of eating the restaurant’s food between Dec. 10 and Christmas Eve.

The Jimmy John’s closed for three days in late December for a special cleaning and disinfection. State officials say no new cases of the illness have been reported since the restaurant reopened on Dec. 27.