An E. coli outbreak has sickened at least 24 people in Michigan, mostly in the southeastern part of the state, health officials announced on Thursday.

The first cases have been reported a few weeks ago at Michigan State University. Soon afterward, new cases have been confirmed in Illinois, Oregon and Ohio, according to the Centers for Disease Control and Prevention.

As stated by Greg Holzman, chief medical executive for the Michigan Department of Community Health (MDCH), all 24 cases point out “a common food source, although we do not know what that food source is at this time." Seven of them have been detected at Michigan State University, five among prisoners at the Lenawee County Jail, three in Macomb County, other three at the University of Michigan; two have been reported in Wayne County and one case per St. Clair and Oakland County.

These cases may be associated with a common food source, the MDCH said. The department will carry on performing tests in order to establish which is in fact the culprit of the three-week E. coli food poisoning outbreak.

Originally, the E. coli is a bacterium that is commonly found in the lower intestine of animals with warm blood. Most E. coli strains are risk-free but some of them could lead to serious food poisoning in humans. The strains that don’t pose any risk are part of the normal flora of the gut and can produce vitamin K, a vitamin which is a regularly given to newborn babies.