(NewsNation) — A major cyclospora outbreak has expanded to four more states, bringing the total number of affected states to nine.

The Centers for Disease Control and Prevention linked cases in Illinois, Kansas, Oklahoma and Pennsylvania to an outbreak potentially caused by shredded lettuce grown in central Mexico.

Previously, cases had been documented in Indiana, Kentucky, Michigan, Ohio and West Virginia.

The Food and Drug Administration also linked the outbreak to distributor Taylor Farms. The company voluntarily recalled products distributed across 27 states and sold to Taco Bell.

Cases of cyclospora typically rise in summer, as the parasite thrives in hot weather, but this year, a record number of cases have been reported.

The CDC has documented more than 4,000 laboratory-confirmed cases and state records suggest the total number of cases could top 11,000.

The parasite is spread by fecal matter and typically winds up on produce when contaminated water is used in farming.

Because of the way it clings to plants, cyclospora is difficult to wash off food. If ingested, it causes illness characterized by explosive diarrhea and gastrointestinal distress.

Cyclosporiasis, the official name for the illness caused by cyclospora, can be treated with antibiotics. If left untreated, illness can last up to a month.

Earlier in the week, the agency announced it was also investigating a second, smaller outbreak of the parasite.