Health officials say they're expanding the investigation into an illness outbreak associated with a suburban Kansas City dinner theater.

The Kansas Department of Health and Environment has been investigating a norovirus outbreak that apparently sickened people after they attended performances at the New Theatre Restaurant in Overland Park.

KDHE initially said the outbreak sickened more than 100 audience members. But KDHE said Thursday so far more than 390 individuals have reported illness. Four people who became ill have laboratory specimens that confirmed norovirus.

The department also asks that people who attended performances from January 15 until the present take part in a confidential online KDHE survey even if they didn't become ill.

KDHE is investigating the source of the illness, which has symptoms including vomiting, diarrhea, fever and body aches.