Federal health authorities are tracking the largest known cyclosporiasis outbreak in U.S. history as case numbers continue to surge across the country.

According to updated data from the Centers for Disease Control and Prevention (CDC), there have been over 6,700 confirmed domestically acquired cases of the gastrointestinal parasitic illness since May 1. With more than 11,500 additional cases pending confirmation, the nationwide total of suspected infections has topped 18,000.

Investigators have linked the core outbreak to contaminated iceberg lettuce imported from Mexico. Nine states are now tied to the source of the outbreak, with Illinois, Kansas, Oklahoma, and Pennsylvania recently added to the list.

Michigan has emerged as the hardest-hit region, reporting more than 10,000 cases—a massive spike for a state that typically sees around 50 cases annually. Ohio has reported the second-highest tally with over 2,600 cases, while Indiana, Kentucky, and Illinois have all seen significant weekly surges.

While every U.S. state has logged at least one cyclosporiasis case this year, not all are tied to the primary produce investigation:

• Domestically Acquired: The CDC has identified domestic cases in 44 states. Outlying states like Maine and Utah report that their sparse cases are separate from the main outbreak, while Hawaii’s infections stem entirely from travel.

• Travel-Related: Beyond the domestic outbreak, over 1,000 laboratory-confirmed cases across 42 states have been traced to international travel, where patients contracted the parasite from contaminated food or water abroad.

Officials note that the official figures likely represent a fraction of the true total, as many infected individuals do not seek medical testing or experience symptoms.

Despite the record-breaking figures and expanding state list, health officials continue to state that the overall U.S. food supply remains safe.