(CNN) -- Diners at Red Lobster and Olive Garden restaurants in Iowa and Nebraska caught an intestinal illness after eating salad mix that came from Mexico, according to the U.S. Food and Drug Administration.
The federal agency said its investigators have traced the outbreak to four "illness clusters" of restaurants, which spokeswoman Theresa Eisenman later identified to CNN as Red Lobster and Olive Garden locations. The probe didn't find indications that any bags of salad mix with the rare type of parasite -- known as cyclospora -- were sold at U.S. grocery stores.
The tainted salad mix came from Taylor Farms de Mexico, "a processor of foodservice salads," according to the FDA.
Darden -- the parent company for Olive Garden, Red Lobster and other restaurant chains such as LongHorn Steakhouse -- described the August 2 announcement from the FDA as "new information."
"Nothing we have seen prior to this announcement gave us any reason to be concerned about the products we've received from this supplier," Darden said in a statement, in which the company insisted "it is completely safe to eat in our restaurants."
Taylor Farms has been cooperating with U.S. officials, the FDA said, adding that tests will be conducted at the company's processing facility in Mexico "to try to learn the probable cause of the outbreak and identify preventive controls." The last inspection there, in 2011, turned no notable problems, according to the federal agency.
The company's CEO, Bruce Taylor, told CNN on Friday night that the company's plant in Mexico produced and distributed about 48 million servings of salads to thousands of restaurants in the Midwest and eastern United States this past June.
"We have an extensive testing program in Mexico to test water sources and raw product for coliforms, E. coli, Salmonella and Listeria," said Taylor. "All our tests have been negative and we have no evidence of cyclospora in our product."
Iowa health authorities said Thursday that the prepackaged salad mix of iceberg and romaine lettuce, carrots and red cabbage was no longer in the state's supply chain.
"Bagged salads and all other vegetables are safe to eat," the state's health department said.
What's happening in that state and Nebraska may be linked to 140 cyclospora cases in Texas, that state's department of health services said Friday. As of then, authorities had not singled out a common source for the Lone Star State's outbreak, which is largely centered in and around Dallas and Fort Worth.
Despite the lack of a connection, a Dallas woman sued Darden on Friday -- soon after the FDA implicated the restaurant company -- "for all general, special, incidental and consequential damages" tied to her July 1 visit to an Olive Garden in Addison, Texas.
Suzanne Matteis contends in her lawsuit that four days after eating spaghetti with meat sauce and a salad from Olive Garden, she suffered severe intestinal issues. She says a clinic near her home took a stool sample and diagnosed her with a cyclospora infection.
Matteis says she's still not feeling completely recovered. "I think I'm getting better, but I still don't have a lot of energy. I'm pooped. I'm worn out," she told CNN.
While he hadn't been aware of the lawsuit until being alerted by CNN, Darden spokesman Mike Bernstein said that his group's restaurants in Texas have a different supplier than its restaurants in Iowa and Nebraska.
The U.S. Centers of Disease Control and Prevention has been collaborating with health officials in numerous states since late June trying to pin down what's causing the spate of cyclospora. As of August 2, the CDC has been notified of 425 cases in 16 states: Arkansas, Connecticut, Florida, Georgia, Iowa, Illinois, Kansas, Louisiana, Minnesota, Missouri, Nebraska, New Jersey, New York, Ohio, Texas and Wisconsin. At least 24 people have been hospitalized, the CDC says.
"It is not yet clear whether the cases from all of the states are part of the same outbreak," the organization says.
People get the disease by eating food or drinking water that's been contaminated with feces with the parasite. The ailment -- which strike in places where cyclospora is common, like tropical or subtropical regions, but is occasionally seen in the United States as well -- causes symptoms such as diarrhea, weight loss and nausea that can last anywhere from a few days to more than a month.
CNN's Amanda Watts and Caleb Hellerman contributed to this report.