Iowa health officials are investigating outbreaks of a parasitic infection that causes intestinal illness and might be linked to McDonald's salads.Iowa has reported 15 cases since late June. Illinois has reported 90 cases since mid-May.As a result, McDonald's is stopping the sale of salads at 3,000 restaurants after people became sick from the parasite, which causes intestinal illness as a result of consuming contaminated food or water.Symptoms can begin a week or more after consuming the parasite. They include diarrhea and frequent, sometimes explosive, bowel movements, according to the U.S. Centers for Disease Control and Prevention.Those who are infected might also experience loss of appetite, weight loss, stomach cramps or pain, nausea, gas and fatigue. Vomiting, headache, fever, body aches and flu-like symptoms can also occur.The illness can last from a few days to a few months, and patients might feel better, then get worse again. Patients can be treated with antibiotics.McDonald's is removing the lettuce blend from identified restaurants and distribution centers. At least one of the affected restaurants is in each of the following states: Illinois, Iowa, Indiana, Wisconsin, Michigan, Ohio, Minnesota, Nebraska, North Dakota, South Dakota, Montana, Kentucky, West Virginia and Missouri.The Iowa Department of Public Health is asking anyone who has eaten a McDonald's salad since mid-June and experienced diarrhea and fatigue to contact a health care provider to be tested and receive treatment."This summer there have been several clusters of cyclospora illness associated with various foods that are commercially available," a statement from the Iowa Department of Public Health said.McDonald's is cooperating with the CDC and U.S. Food and Drug Administration in investigating the outbreak, according to the Iowa Department of Public Health.McDonald's said in an email it has been in contact with public health authorities from Iowa and Illinois about an increase in cyclospora infections."Out of an abundance of caution, we decided to voluntarily stop selling salads at impacted restaurants until we can switch to another lettuce blend supplier," the email said. "We are in the process of removing existing salad blend from identified restaurants and distribution centers -- which includes approximately 3,000 of our U.S. restaurants primarily located in the Midwest."The parasite cyclospora is the culprit behind an ongoing outbreak linked to recalled Del Monte Fresh vegetable trays; it's linked to more than 200 illnesses in four states.The parasite is also to blame for an outbreak in Texas, although officials have not yet identified what's making people sick there.