(CNN/RNN) - Two states are investigating whether McDonald's salads are linked to a parasite that's sickened more than 100 people.
Both the Illinois and Iowa departments of health said they are looking into outbreaks of an intestinal illness.
The Illinois Health Department said a quarter of its cases reported eating McDonald's salads before falling ill.
Investigators are looking at the cyclospora parasite, which causes intestinal illness. The parasite is usually found in tropical areas but in the U.S. has been linked to imported produce, the Centers for Disease Control and Prevention said.
Both states said McDonald's is cooperating with both the CDC and the FDA in investigating the illnesses.
In a statement, McDonald's says it will voluntarily stop selling salads at its affected restaurants but will resume salad sales there once they change their lettuce blend supplier.
Symptoms, which occur a week after consuming the parasite by food or water, include diarrhea, frequent and sometimes explosive bowel movements, according to the CDC. Other symptoms include stomach cramps, nausea, fatigue and fever.
Those with healthy immune systems should recover without treatment, the CDC said. Those with a weaker immune system should see a doctor because the illness could be prolonged or severe.