CHICAGO (AP) — Illinois reported one new case of a rare stomach illness Monday, bringing the total number of cases in the state to five.

Health officials investigating the cases have been unable to track the illness to any particular food source, said Illinois Department of Public Health spokeswoman Melaney Arnold. The cases are spread out in five separate counties, making it difficult to find a culprit.

An outbreak of the same stomach illnesses in Iowa and Nebraska has been linked to salad mix served at local Olive Garden and Red Lobster restaurants and supplied by a Mexican farm. Recent cyclospora infections have sickened more than 400 people in 16 states.

“We are unable to confirm a link to bagged salad because we have not had any restaurant clusters or grocery store clusters and our cases do not remember which brand of bagged salad they may have eaten,” Arnold said Monday.

“It’s difficult to identify a source when there is only one case in each of the areas,” Arnold said.

In Illinois, none of the people infected has required hospitalization. The cases of cyclosporiasis were reported in Montgomery, Jo Daviess, Lake, Sangamon and McHenry counties.

The most recently reported case is in McHenry County. That person got sick the third week of July.

Illinois health officials believe the Sangamon County patient acquired the infection in Iowa and they have provided information on that case to Iowa health officials, Arnold said.

The illness is caused by a microscopic parasite. People get sick when they consume contaminated food or water. After exposure, people usually get sick after about a week and have diarrhea and other flu-like symptoms that can last from a few days to a month or longer if untreated. The illness is not generally contagious and can be treated with antibiotics.

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