DES MOINES, Iowa (AP) — Illinois and Iowa health officials are investigating an increase in people becoming sick from the parasite Cyclospora.

The Iowa Department of Public Health issued a news release Thursday saying the illnesses appear to be connected to consumption of salads from McDonald’s restaurants.

The department says the Illinois Department of Public Health has noted a similar increase in cases. IDPH officials say about 90 people came down with the illness and started getting sick around mid-May.

About a quarter of the victims say they ate McDonald’s salads, but investigators are looking into other sources, as well.

McDonald’s is pulling the salads and replacing them with products from other sources.

The Iowa department says it has identified 15 Iowa residents who ate McDonald’s salads in late June to early July prior to getting ill.

The department says McDonald’s is also investigating and has been fully cooperating with health officials.

Cyclospora is a parasite commonly found in developing countries.

The intestinal illness is caused by consuming food or water contaminated with the microscopic parasite.

The main symptom is watery diarrhea lasting a few days to a few months.

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