The Centers for Disease Control and Prevention (CDC) expanded the outbreak of cyclosporiasis linked to shredded iceberg lettuce to an additional four states, a CDC official told ABC News on Friday.
This means there are now nine states in the outbreak with Illinois, Kansas, Oklahoma and Pennsylvania joining Indiana, Kentucky, Michigan, Ohio and West Virginia.
The majority of cases have been reported in Michigan, where there are now 8,176 cases, according to an update Friday from the Michigan Department of Health and Human Services (MDHHS) with about 160 hospitalizations.
So far, the CDC has confirmed cases among 1,947 people, but the agency wrote on its website that the outbreak "may not be limited to the states with known illnesses, and the true number of sick people is likely much higher than the number reported."
This is because many people recover on their own without receiving medical care and are not tested for the parasite, according to the CDC.
The outbreak has been linked to shredded iceberg lettuce at some Taco Bell restaurants, which was supplied by Taylor Farms and sourced from central Mexico.
Last week, Taylor Farms de Mexico issued a voluntary recall of all iceberg lettuce sourced from central Mexico, with the recall affecting 27 states. The recalled products were distributed from June 29 through July 16 and have a best-if-used-by dates up to Aug. 3.
Taco Bell said Friday that it is no longer using lettuce from Taylor Farms de Mexico at any of its restaurants.
Over the weekend, the FDA said a sample of shredded iceberg lettuce supplied by Taylor Farms, which was not part of the recall, tested positive.
However, the agency later clarified that during a re-review of the sample results, it determined the result was a false positive. Taylor Farms issued a statement on Sunday, saying "we were informed that FDA made a mistake."
Acting FDA Commissioner Kyle Diamantas said during a press conference on Monday that the false positive did not change the FDA's findings that linked cases to shredded lettuce from Taylor Farms.
The CDC said it is also investigating other outbreaks and illnesses of cyclosporiasis nationally that are unrelated to the nine-state outbreak.
Since May 1, cases of cyclosporiasis have topped 11,500 in 41 states, according to data updated by the CDC on Wednesday.
There are at least 4,173 laboratory-confirmed cases of cyclosporiasis, including 308 hospitalizations, the data shows.
The agency is also aware of at least 7,400 additional cases that have not yet been laboratory confirmed.
ABC News' Youri Benadjaoud contributed to this report.
