The Subway on Roosevelt Road in Lombard is closed while an investigation is underway.
DuPage County health officials say some of the illnesses were caused by shigellosis. Symptoms include diarrhea, vomiting, fever and stomach cramps. Four people have been hospitalized.
Anyone who became sick after eating at that subway restaurant between February 24th and March 1st should see a doctor and report the illness to the health department.