The massive, multistate outbreak of cyclosporiasis has expanded to nine states, the Centers for Disease Control and Prevention said Friday.

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Outbreaks in Illinois, Kansas, Oklahoma and Pennsylvania have now been connected to cases in Indiana, Kentucky, Ohio and West Virginia, as well as hard-hit Michigan.

The discovery doesn’t necessarily mean that cases are accelerating, but provides a clearer picture of what’s been so unusual about the record high number of cyclosporiasis cases this summer.

“We’re getting more complete case data that covers the range of the outbreak,” said Gwen Biggerstaff, CDC’s deputy director of the department of foodborne, waterborne and environmental diseases. “States are completing interviews with people, and we’re filling in the data.”

The CDC has confirmed 1,947 cases in those nine states. Shredded iceberg lettuce sourced from Taylor Farms de Mexico is the likely source, the Food and Drug Administration said last week. The company voluntarily recalled the product from the U.S. market.

“We know it went to many states, to many points of sale,” said Kari Irvin, deputy director of FDA’s Coordinated Outbreak Response and Evaluation Network. The FDA watches the CDC’s confirmed case counts closely, she said, “because it will help tell us if the recall is enough, that they’ve recovered all products that need to be removed from the market.”

The clue that linked cases to Taylor Farms came from interviews with people who got sick. Many said they’d eaten at Taco Bell in June, before the waves of cases took off. The restaurant chain pulled lettuce from its menu ahead of the recall from Taylor Farms.

Irvin said FDA investigators are working to determine whether additional growers might have played a role. “The data that we have now really continues to home in on growers that were already identified.”

The outbreak expanding to four more states was first reported by The Washington Post.

Cyclosporiasis is a foodborne infection caused by a parasite that likes to cling to fresh produce, including fruit, vegetables and herbs, making them difficult to wash away. The parasite, called cyclospora, spreads through water contaminated with human feces.

Iceberg lettuce from Taylor Farms is unlikely to be the only product making people sick. There are nearly 12,000 confirmed or suspected cases of the illness nationwide, according to tallies from the CDC and state health departments. Michigan has had the brunt of cases, with nearly 8,000 infections. The CDC has sent three staffers to Ohio, which has 2,596 cases, to help with that state’s investigation.

Hundreds of other cases have been reported in states not linked so far to the multistate outbreaks.

New York has had 632 cases since May, and North Carolina has reported 561 during the same time frame. Preliminary investigations into North Carolina’s outbreak suggests parsley and cilantro could be behind those cases.

The FDA’s Irvin said the agency has seen different “signals” of outbreak sources. “We have multiple investigations of cyclospora open,” she said.