Cases of cyclosporiasis, an intestinal illness caused by a single-celled parasite, have surged in recent weeks, and some cases have been linked to McDonald’s salads by state departments of public health in Illinois and Iowa. According to the Wall Street Journal, one-fourth of the 90 cases of cyclosporiasis reported in Illinois have been linked to McDonald’s salads, while 15 cases have been linked to the salads in Iowa.

Those cases were announced earlier this week. Now, McDonald’s, out of what it describes as “an abundance of caution,” has stopped serving salads at restaurants in Iowa and Illinois, as well as at other restaurants that had received shipments from the same supplier. Those restaurants are in Indiana, Wisconsin, Michigan, Ohio, Minnesota, Nebraska, South Dakota, Montana, North Dakota, Kentucky, West Virginia, and Missouri.

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Cyclosporiosis causes extremely unpleasant symptoms including nausea and diarrhea, but is not generally fatal. It is spread primarily through human fecal matter, particularly on raw vegetables. Washing food is not known to be effective in preventing transmission.

Other cyclosporiasis cases have recently been linked to Del Monte vegetable snacks sold in convenience stores, also concentrated in the upper Midwest. According to the FDA, there is no evidence directly connecting those cases with the McDonald’s cases, and McDonald’s told the Journal that Del Monte was not a supplier for the salads in question.

The fast-food chain says it will switch to a new supplier for its salads.