Seven people have been sickened and four were hospitalized in an outbreak of E. coli O157:H7 linked to a restaurant in Houghton, Michigan.

According to a story Friday in the Mining Gazette, some of the illnesses were lab-confirmed earlier this month, which alerted health department officials to the outbreak.

So far, according to the newspaper, the common factor linking the E. coli infections is that those sickened ate at the Ambassador Restaurant. Dr. Terry Frankovich, Western Upper Peninsula Health Department medical director, said the source of the infection was apparently an ill food handler who was asymptomatic.