The Centers for Disease Control and Prevention (CDC) has expanded its warning over the largest Cyclospora outbreak reported in the United States this year, saying the foodborne illness has now spread across nine states as investigators continue working to identify and contain its source.FILE - This undated photo taken through a microscope provided by the CDC shows Cyclospora cayetanensis oocysts found in a fresh stool sample. (CDC via AP)Cyclospora is a microscopic parasite that spreads through contaminated food or water and causes cyclosporiasis, a gastrointestinal illness that can trigger severe diarrhea, stomach cramps, nausea, fatigue and loss of appetite.While some patients have required hospitalization, no deaths linked to the outbreak have been reported this year.Which states are affected?In a Friday update, the CDC said the outbreak now spans nine states:IllinoisIndianaKansasKentuckyMichigan (the hardest-hit state)OhioOklahomaPennsylvaniaWest VirginiaWhat is causing the Cyclospora outbreak?Federal health officials have identified shredded iceberg lettuce supplied by Taylor Farms as the likely source of the multistate outbreak.According to the Food and Drug Administration (FDA), the lettuce was distributed to Taco Bell restaurants where many infected people reported eating before becoming ill. Following the investigation, Taylor Farms voluntarily recalled all shredded iceberg lettuce sourced from its Guanajuato, Mexico, facility, while Taco Bell removed the affected lettuce from its restaurants.Also Read: Taco Bell removes Taylor Farms lettuce amid cyclosporiasis outbreak; producer issues clarification: ‘We are committed…’The CDC said 1,947 infected people across the nine affected states reported eating at Taco Bell before falling ill. Illnesses linked to the lettuce outbreak have been reported between June 22 and July 20, though the agency noted that federal case counts may lag behind reports from individual states.The CDC also said the current outbreak is already the largest multistate cyclosporiasis outbreak recorded in the US this year, with thousands of illnesses reported nationwide. This is far above the roughly 200 to 1,000 cases typically reported annually.Investigation still underwayThe FDA is simultaneously investigating a separate Cyclospora outbreak tied to an unidentified food item.Meanwhile, Mexican health authorities said samples of lettuce and water collected from Taylor Farms' facility in central Mexico tested negative for Cyclospora. However, US regulators said those findings do not rule out the company's products as the likely source because the suspected contaminated crop had already been harvested and distributed before the testing took place.Also Read: Taylor Farms: All about the Taco Bell lettuce supplier linked to US cyclosporiasis outbreakTaylor Farms has also faced criticism over its handling of the recall. Some public health experts argued that the company's recall notice made it difficult for consumers to identify whether they had purchased affected products.The company also drew scrutiny after stating that the FDA had apologized over an earlier false-positive lettuce sample. The FDA later clarified that it had not apologized and reiterated that Taylor Farms' shredded iceberg lettuce remains the most likely source of the outbreak.Taylor Farms subsequently removed that statement from its X account, though it remains available on the company's website.Taylor Farms supplies produce to major retailers, including Walmart, Target and Whole Foods, as well as restaurant chains such as Taco Bell.