The cyclosporiasis outbreak that’s sickened thousands of people in the US is spreading further, as federal health officials linked four more states to tainted iceberg lettuce imported from Mexico.

The US Centers for Disease Control and Prevention tied Illinois, Kansas, Oklahoma and Pennsylvania to the surge in cases that originally emerged in Michigan, it said on Friday. The CDC linked nearly 2,000 cases in nine states to the lettuce, including Indiana, Kentucky, Ohio and West Virginia, with thousands more people reporting infections to their local health departments.

US authorities previously tied the illnesses in the Midwest to lettuce supplied by Taylor Farms to Taco Bell. Taylor Farms recalled products sent to 27 states and suspended all iceberg lettuce sourcing from central Mexico, as well as production there. The CDC and Food and Drug Administration said people should throw away the recalled lettuce.

“We’ve commissioned independent experts to conduct a top-to-bottom review of food safety processes and protocols in our central Mexico facility,” the company said. “We continue to work with health authorities, customers, and independent farming partners to address this issue.”

Infections from the diarrhea-causing cyclospora parasite increase in the warmer summer months, and new cases continue to emerge in other parts of the country. At least 41 states have reported infections in recent weeks and more than 300 people have been hospitalized, according to the CDC.

North Carolina health officials reported more than 560 infections since July 20, and said Friday that some were linked to parsley, cilantro and lettuce. It’s not part of the original Midwest cluster connected to Taco Bell, the health department said.

The FDA is investigating another cyclospora outbreak, with 72 cases tied to an unknown source, the agency said on Wednesday.

Mexican authorities said late Thursday that tests on lettuce and water samples from a Taylor Farms facility in Mexico were negative for cyclospora. The FDA previously reported a false positive on the company’s lettuce, though it said Friday “this false-positive lab sample DOES NOT change the basis for FDA’s ongoing outbreak investigation or the overwhelming epidemiological data supporting the current voluntary recall by Taylor Farms.”

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