(CNN) - Federal health officials reported Thursday an additional 109 cases of cyclospora infection in an ongoing outbreak linked to McDonald's salads that began in May.
The total number of laboratory-confirmed illnesses from this outbreak is now 395, according to a statement from the US Food and Drug Administration. At least 16 of the sick individuals have been hospitalized.
The cyclospora parasite causes intestinal illness in people who consumed 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 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 a few days to a few months, and patients might feel better but then get worse again. Cyclosporiasis can be treated with antibiotics.
Illnesses have been reported in 15 states: Connecticut, Florida, Iowa, Illinois, Indiana, Kentucky, Michigan, Minnesota, Montana, Nebraska, Ohio, South Dakota, Tennessee, Virginia and Wisconsin. However, the patients in Connecticut, Michigan, Tennessee and Virginia bought their salads in Illinois while traveling, and the Florida patient bought the salad in Kentucky.
The FDA said an unused package of a Fresh Express salad mix of romaine lettuce and carrots that had been distributed to McDonald's tested positive for the presence of Cyclospora though it was past its July 19 expiration date.
"Epidemiologic evidence indicates that salads purchased from McDonald's restaurants are one likely source of these infections. The investigation is ongoing, and FDA is working to determine the sources of the ingredients that were in common to the salads served at McDonald's," the CDC said in an outbreak update posted on its website Thursday.
McDonald's said in a statement on July 13 that it had removed the salad mix from it's impacted restaurants and replaced it with a different supplier.
In a recall statement on the Fresh Express website, the company said it had launched a "precautionary recall" of the institutional food service product on July 27 of a "limited number of cases."
The statement said, "Fresh Express follows rigid food safety requirements and preventive controls throughout our supply chain that are carefully designed to mitigate against potential health risks."
The company's salad mix recall was connected with a public health alert issued Monday by the US Department of Agriculture's Food Safety and Inspection Service advising consumers that certain salad and wrap products might be contaminated with cyclospora. The products were sold by grocery stores including Kroger, Trader Joe's and Walgreens.
In the alert, the USDA said the issue was discovered when Indianapolis-based food distributor Caito Foods "received notification from their lettuce supplier, Fresh Express, that the chopped romaine that is used to manufacture some of their salads and wraps was being recalled."
The lettuce from McDonald's that tested positive for the cyclospora parasite was in the same lot as the lettuce distributed to Caito Foods, the CDC said Wednesday. "Fresh Express also reported that no romaine lettuce from the lot that was positive for cyclospora was packaged for direct retail sale to consumers," the CDC said.
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