Public health officials in Illinois and Iowa have reported a surge 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.

“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,” Dr. Nirav D. Shah, the director of the Illinois Department of Public Health, said on Thursday.

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

“McDonald’s is committed to the highest standards of food safety and quality control,” the company said in a statement. “We are closely monitoring this situation and cooperating with state and federal public health authorities as they further investigate.”

Cyclosporiasis is caused by a microscopic parasite, known as cyclospora, found in food or water that has been contaminated with feces. Although rarely fatal, the infection can cause severe nausea, fatigue and diarrhea for more than a week. Symptoms typically appear within a few days of infection.

Health officials in both Illinois and Iowa said that people who experienced similar symptoms after eating at McDonald’s should contact a doctor for testing and possible treatment.

The cases in Illinois first appeared in mid-May, while the illnesses in Iowa were more recent, surfacing in late June and early July.

They were announced as state and federal health authorities investigate another outbreak of 225 cases in Illinois, Indiana, Iowa, Michigan, Minnesota and Wisconsin that have been tied to Fresh Del Monte Produce vegetable trays.

Cyclosporiasis has been reported in the United States since the mid-1990s, after the country started to import significantly more food, particularly fresh fruit and vegetables. The Centers for Disease Control and Prevention has investigated more than 2,000 cases of cyclosporiasis since 2000. Past outbreaks have been blamed on basil from Peru, snow peas from Guatemala and cilantro from Mexico.