At least 22 people on the Fond du Lac Reservation experienced foodborne illness linked with E. coli bacteria, a spokesperson with the Minnesota Department of Health said Wednesday.

The news was first posted on the band’s website Tuesday, when it indicated there were several cases. The band is cooperating with the state health department’s investigation, which has yet to pinpoint a cause of the contamination.

The strain is believed to be E. coli O157, commonly associated with ground beef, said the spokesperson. The strain that prompted Applebee’s restaurants to adjust its Minnesota menus earlier this month was E. coli O111, the spokesperson said as a way of comparison. The restaurant chain voluntarily changed a supplier as well as removed its Oriental Chicken Salad and other nuts and leafy vegetables from its Minnesota menus in that instance.

Health department spokesman Doug Schultz said the 15 people reported ill in that case was “probably the tip of the iceberg.”

Schultz explained that Minnesota is a “real-time investigation” state, placing it at the forefront of reactions to foodborne illness. The goal of a real-time investigation is to arrest the spread of illness by pulling potentially contaminated fare, rather than other states, which conduct follow-up investigations.