Investigations into the largest cyclosporiasis outbreak on record expanded to nine states this week, as more than 11,500 people are suspected to have been sickened this summer, according to reports and the Centers for Disease Control and Prevention (CDC).

Data released by the CDC this week said the agency is looking into 4,173 laboratory-confirmed domestic cases of the disease and investigating an additional 7,400.

Additionally, the Washington Post reported that the CDC’s five-state investigation into cyclosporiasis cases – already the largest on record – had expanded to four more states for a total of nine.

Iceberg lettuce served at Taco Bell restaurants was linked to cyclospora cases in the first five states – including in Indiana, Kentucky, Michigan, Ohio and West Virginia. More states now included in the investigation include Illinois, Kansas, Oklahoma and Pennsylvania. The iceberg lettuce was linked to a single supplier, Taylor Farms de Mexico, which has issued a voluntary recall.

Cyclosporiasis is the illness caused by the parasite cyclospora, a microscopic protozoa that is known to contaminate raw produce that comes into contact with feces. Symptoms of the disease include explosive and watery relapsing diarrhea that can last weeks.

In addition to expanding the search for contaminated produce to more states, the US Food and Drug Administration (FDA) updated its website on Thursday to reflect a separate investigation into 72 cyclosporiasis cases. It has not yet linked the cases to a specific product or products.

Smaller outbreaks across the country, for example in North Carolina, have linked cyclosporiasis cases to parsley and cilantro, both of which are commonly served raw.