The U.S. Centers for Disease Control and Prevention (CDC) is warning people not to eat shredded iceberg lettuce served at Taco Bell locations in Indiana, Kentucky, Michigan, Ohio and West Virginia.
The warning, posted Thursday night, follows an outbreak of cyclosporiasis that has sickened more than 1,644 people who reported eating at the chain's restaurants in those five states, according to the CDC.
Of those, 94 have been hospitalized. No deaths have been reported. No recall has been issued, and the investigation remains open, The New York Times reported.
The lettuce was grown by a single supplier in Mexico, the U.S. Food and Drug Administration (FDA) said. The agency has increased screening of the company's lettuce at the border and warned that other restaurants and stores could be implicated as the investigation continues.
Not every Taco Bell in the five states received the affected lettuce.
