The DuPage County Health Department is investigating the cause of food-related illnesses traced to a Subway restaurant in Lombard.

A cluster of gastrointestinal illnesses has been traced primarily to customers of the sandwich shop at 1009 E. Roosevelt Road in Lombard, according to a health department news release. The restaurant has been closed and its owners, along with corporate representatives, have been helping in the investigation.

Although the investigation is still underway, preliminary information shows the outbreak of illness is shigellosis, from a group of bacteria called Shigella, officials said. The illness can lead to diarrhea, vomiting, fever and stomach cramps one to two days after being exposed.

As of today, eight cases have been confirmed. Four people had to be hospitalized, although one of them has been discharged and is recovering at home.

The bacterium can be acquired from eating contaminated food, and also can be spread from contact of contaminated human waste. Anyone with the illness should not prepare food for others, and anyone contacting an infected person should follow careful hygiene habits, officials said.