More than 100 people in the Midwest have been infected by an intestinal parasite in recent weeks that has been tied to the consumption of salads at McDonald’s, health experts announced this week.

Public health officials in Illinois and Iowa have reported a spike in cases of cyclosporiasis, with at least 15 infections in Iowa and 90 others in Illinois. Everyone who became ill in Iowa and about a quarter of those who became sick in Illinois said they had eaten McDonald’s salads in the days before symptoms appeared, according to the states’ health departments. According to the Minnesota Department of Health, three cases have occurred in Minnesota.

“Although a link has been made to salads sold in McDonald’s restaurants in some Illinois cases, public health officials continue to investigate other sources,” said Dr. Nirav D. Shah, director of the Illinois Department of Public Health.

McDonald’s said Friday that “out of an abundance of caution,” it had stopped selling salads at about 3,000 restaurants in the Midwest and was working to remove the lettuce from those locations. The company said it was switching to another lettuce supplier at those locations.

Cyclosporiasis is caused by a microscopic parasite, cyclospora, found in food or water that has been contaminated with feces. While rarely fatal, the infection can cause severe nausea, fatigue and diarrhea for more than a week.