GRAND RAPIDS, Mich. (WOOD) — The Michigan Department of Health and Human Services said in over half of cases in the Michigan E. coli outbreak, patients reported eating at Wendy’s fast-food restaurants.

In a Friday press release, MDHHS said that there were 43 confirmed shiga toxin E. coli cases in the state. The illnesses happened in late July through early August in 18 jurisdictions. Cases were reported in Allegan, Branch, Clinton, Genesee, Gratiot, Jackson, Kent, Macomb, Midland, Monroe, Muskegon, Oakland, Ogemaw, Ottawa, Saginaw Washtenaw, and Wayne counties.

The health department said that more than 55% of the patients in cases in Michigan reported consuming food at Wendy’s restaurant locations. However, there is no recommendation to avoid Wendy’s.

Investigators have not identified a specific food item that caused the illness, but they are focusing on sandwiches that had romaine lettuce. Wendy’s is working with local public health departments to remove any products under suspicion.

The E. coli outbreak has been affecting people ages 6 to 94 years old. Fifty-six percent of people with the infection have been hospitalized. Four cases of hemolytic uremic syndrome, a complication related to shiga toxin E. coli infections, have also been identified.

Symptoms of E. coli infection typically appear three to four days after the exposure and usually improve in five to seven days.

MDHHS reminds Michigan residents to seek medical attention if they experience symptoms such as severe stomach cramps, diarrhea, vomiting or other gastrointestinal distress. It also urged people to take proper precautions when they are handling food.

For more information on E. coli, visit the USDA website on protection from foodborne illness or the CDC website on prevention. Find food safety information on the Michigan Department of Agriculture and Rural Development website.