The number of people infected with a parasite linked to McDonald’s salads has grown to 476, the U.S. Food and Drug Administration said Thursday.

The lab-confirmed cases of Cyclospora infection were reported in 15 states, with 21 people now hospitalized. The ill range in age from 14 to 91, with two-thirds of them women.

The FDA continues to investigate and is “currently reviewing distribution and supplier information for romaine and carrots,” the agency said in its latest update.

The investigation is ongoing and the #FDA is currently reviewing distribution & supplier info for romaine & carrots.

Consumers with Cyclospora symptoms (diarrhea, loss of appetite, nausea) should contact their healthcare provider. https://t.co/WuIPaThcMf — FDA FOOD (@FDAfood) August 17, 2018

The probe has focused on Fresh Express salad mix containing those two ingredients. Health officials tested an unused package of the mix, which had been sent to McDonald's, and found Cyclospora in that sample.

The fast food chain voluntarily stopped selling the lettuce blend at “impacted restaurants” — about 3,000 locations, mostly in the Midwest — on July 13 and has since turned to a new salad supplier, McDonald’s said in a statement.

No products have been recalled. Fresh Express told the FDA that the romaine lettuce from the same lot as the positive sample was not sold in retail stores and had already expired. The carrots in the mix were only sent to McDonald's.

That same supplier was part of a July health alert involving chopped romaine used in pre-made salads and wraps sold at stores including Trader Joe's, Kroger and Walgreens.

The illnesses started in May, but people who were sickened after July 5 might still not be in the case count because of the time it takes to report an illness after a person becomes infected, the Centers for Disease Control and Prevention noted. For Cyclospora infections, this can take up to six weeks.

Cyclospora cayetanensis is a tiny parasite that can cause an intestinal illness when it contaminates food or water.

Symptoms of cyclosporiasis include diarrhea, “with frequent, sometimes explosive, bowel movements,” the FDA noted. Infected people can also experience loss of appetite, weight loss, stomach cramps, vomiting and fever. Some people have no symptoms at all.