The Centers for Disease Control and Prevention is warning consumers and retailers in eight Midwestern states to stay away from some bagged salad mixes as officials investigate an outbreak of an intestinal illness caused by a microscopic parasite.
More than 200 people in Illinois, Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota and Wisconsin who reported eating the salad mixes before getting sick have lab-confirmed infections of the illness, cyclosporiasis, the C.D.C. said on Friday. At least 23 people have been hospitalized for the illness, and no deaths have been reported, the agency said.
The C.D.C. urged consumers and retailers not to eat, sell or serve four different salad kits that have been recalled, all of which were produced by Fresh Express in Streamwood, Ill.
The products include Marketside-brand Classic Iceberg Salad, which was sold at Walmart stores with use-by dates of May 19 through July 4, and Little Salad Bar-brand Garden Salad, which was sold at Aldi stores with use-by dates of May 1 through June 29. Also on the list were Jewel-Osco Signature Farms-brand Garden Salad with use-by dates of May 16 through July 4, and Hy-Vee-brand Garden Salad with any use-by date.
Fresh Express announced a separate voluntary recall on Saturday of dozens of products produced in Streamwood that contain iceberg lettuce, red cabbage and carrots, after it learned from the F.D.A. that the products may be linked to the outbreak.
The products are marked with the letter Z at the beginning of the product code, which is stamped in the upper right-hand corner of the front of the package, the company said.
People began getting sick from May 11 to June 17, according to the C.D.C. They range in age from 16 to 92 years old; more than half are women and girls.
Cyclosporiasis can be treated with an antibiotic, the agency said, but it noted that most healthy people recover on their own.
The C.D.C. said in its alert that “bagged salad mixes purchased at Aldi, Hy-Vee, Jewel-Osco and Walmart do not explain all of the illnesses in this outbreak,” and added that it and the F.D.A. “continue to investigate to determine whether other products are a source of illnesses.”
Donald W. Schaffner, a food microbiologist at Rutgers University in New Jersey, said that the first major outbreak of cyclosporiasis linked to food was reported in the mid-1990s, and that to this day scientists have yet to figure out what caused it.
“It’s likely due to the quality of the water used to irrigate the produce, and it probably has something to do with human fecal contamination of that water, but of course there’s a whole lot of unknowns,” Professor Schaffner said. “Very often with these fresh produce outbreaks, we never learn the definitive cause.”
“But obviously there was some breakdown in the quality chain,” he added. That hundreds of people are getting sick in multiple states, he said, suggests “some rather significant sanitary breakdown in the production of this food.”
Professor Schaffner said this was the third year in a row that there had been a cyclosporiasis outbreak during the warmer months.
Barbara Hines, a spokeswoman for Food Express, said on Sunday that “while all involved are hopeful the outbreak is waning, the exact source of contamination has not yet been identified, and doing so is imperative.”
“Unfortunately, little is still known about Cyclospora and how it is transmitted to fresh produce, its mode of infection or why outbreaks typically occur during spring and summer months,” she said.
Ms. Hines said the company’s “first concern, of course, is for the health and well-being of those who have become ill, and to ensure all appropriate measures are in place to protect public health.”