A large outbreak of cyclosporiasis associated with iceberg lettuce has been linked to another four states, according to the Centers for Disease Control and Prevention.
At least 1,947 people have become ill and 98 have been hospitalized in the outbreak, which has expanded to include Illinois, Kansas, Oklahoma and Pennsylvania. Michigan, Ohio, Indiana, Kentucky and West Virginia were already part of the outbreak.
The Food and Drug Administration has linked the infections to iceberg lettuce supplied by Taylor Farms and grown in central Mexico. On July 17, Taylor Farms recalled bagged iceberg lettuce sold in 27 states (including the nine states in the outbreak). The recalled lettuce was sent to restaurants, retail stores and food service distributors including Taco Bell and Walmart, but Taylor Farms has not provided clear information about exactly where the products were sold or served, and which specific products were affected.
The news comes as federal officials investigate other cyclospora outbreaks and illnesses across the country, which they say are unrelated to this outbreak. On Thursday, the F.D.A. announced a new outbreak with 72 cases, but did not identify the location or the potential source.
Nationwide, the C.D.C. has confirmed or is investigating more than 11,500 cases of cyclosporiasis, which is caused by a parasite typically spread through food or water contaminated with human feces.
In Michigan, which has reported the most cases, some labs have started to run out of the reagents that they need to test for cyclosporiasis, said Dr. Natasha Bagdasarian, the state’s chief medical executive. Cases there climbed to 7,664 on Thursday — a tally that was “likely an undercount,” Dr. Bagdasarian said, given the shortage of lab supplies.
On Friday, Sean Doyle, a spokesman for North Carolina’s health department, said that investigators there had not yet identified a single source of cyclosporiasis, but that parsley, cilantro, berries and romaine lettuce had come up most often during interviews with sick patients.
Mr. Doyle said that this wasn’t proof that those items were causing illnesses and that, relative to the other items on the list, berries were less likely to be the source.
On Tuesday, cases in North Carolina rose to 561 from 307 a week before.
This has been the worst year on record for cyclosporiasis in the United States, which has seen an average of about 2,800 cases per year nationwide since 2016. Because the parasite thrives in warmer temperatures, cases typically rise between May 1 and Aug. 30. Even so, this year’s count is far higher than the usual summer surge.
The true number of people with cyclosporiasis is likely far higher than the C.D.C.’s current case count, health experts say. Many people with symptoms never get tested. And because it takes time for state health departments to report case numbers to the C.D.C. — and for the agency to confirm them — state totals often exceed those reported by the federal government.
The New York Times reached out to state health departments for their case numbers, which totaled nearly 15,000 as of Friday morning.
Cases of cyclosporiasis have continued to rise in the nine states included in the newly expanded outbreak. Health officials in Ohio confirmed 2,576 cases on Thursday — more than double the number recorded on July 14. Indiana reported 684 cases on Thursday, more than triple the case count from July 14.
On Friday, the F.D.A. said that the number of confirmed cases was expected to continue rising despite Taylor Farms’ recall. The agency said it can take as long as six weeks for the C.D.C. and state officials to determine if a sick person is part of the outbreak.
