New reports say that Norovirus is likely to blame for making about 100 people sick after they ate at a Weston Jimmy John’s, a health official said Wednesday.

Since April 7, the Marathon County Health Department has been receiving reports from people who said they got food from the sandwich shop and then fell ill, said Dale Grosskurth, the department’s environmental health and safety coordinator.

The department is conducting a foodborne illness outbreak investigation in response to the complaints. Investigators have heard from about 100 people with norovirus symptoms, and stool samples from some of them tested positive for the virus, Grosskurth said.

A Jimmy John’s employee also tested positive for norovirus, according to Brian Macak, who owns the franchise at 3910 Schofield Ave.

Norovirus causes severe stomach flu, including diarrhea, abdominal cramps, vomiting, low fever, headaches and chills. It develops a day or two after infection and can be extremely contagious.