(CNN) -- Federal health officials reported Thursday an additional 123 cases of cyclospora infection in an outbreak linked to McDonald's salads that began in May.
The total number of laboratory-confirmed illnesses from this outbreak is now 286, according to the US Centers for Disease Control and Prevention. At least 11 of the sick individuals have been hospitalized.
The cyclospora parasite causes intestinal illness in someone 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 CDC. 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.
The earliest reported illnesses in this outbreak began with symptoms May 20, and the most recent reported cases began June 29.
"Illnesses that started after June 14, 2018, might not have been reported yet due to the time it takes between when a person becomes ill and when the illness is reported. For cyclospora infections, this can take up to six weeks," the CDC said. Therefore, the number of cases is likely to increase.
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 source of the outbreak has yet to be determined. The US Food and Drug Administration said it "is working with McDonald's to identify the common ingredients in the salads identified by those who became sick and to trace back those ingredients through the supply chain."
On July 13, McDonald's said it was removing its lettuce blend from approximately 3,000 locations in 15 states as a precaution. On July 20, the company said the blend was replaced with lettuce from a different supplier.
The CDC and the FDA said this outbreak is not connected to an ongoing outbreak of cyclosporiasis caused by Del Monte Fresh vegetable trays in Iowa, Wisconsin, Minnesota and Michigan.