WASHINGTON -- The Food and Drug Administration says an outbreak of stomach illnesses in Iowa and Nebraska is linked to salad mix served at Olive Garden and Red Lobster restaurants in those states and supplied by a Mexican farm.
The outbreak of cyclospora infections has sickened more than 400 people in 16 states in all.
The agency says it is working to determine whether the salad mix is the source of illnesses in the other 14 states.
"It is not yet clear whether the cases reported from other states are all part of the same outbreak," the agency said in a statement. "The investigation of increased cases of cyclosporiasis in other states continues."
The FDA said its investigation has not implicated any packaged salad sold in grocery stores.
Both Olive Garden and Red Lobster are owned by Orlando-based Darden Restaurants. In a statement, Darden spokesman Mike Bernstein said the FDA's announcement is "new information."
Mr. Bernstein added, "Nothing we have seen prior to this announcement gave us any reason to be concerned about the products we've received from this supplier."
The FDA said it traced illnesses from the restaurants in Nebraska and Iowa to Taylor Farms de Mexico, the Mexican branch of Salinas, Calif.-based Taylor Farms.
The company, which provides produce to the food service industry, said its facility located about 180 miles north of Mexico City in San Miguel de Allende is the only one of its 12 sites to be connected to the cases.
In a statement on the company's website, Taylor Farms says the Mexican facility is "state of the art and has an exceptional food safety record."
The statement said the company is working with FDA investigators, who are looking at the facility, and that the product is out of the food supply.
The FDA said it had audited the Mexican processing facility in 2001 and found "no notable issues." The agency said it would increase surveillance efforts for green leafy products imported from Mexico.
The most recent known illness in the two states linked to the infected salad was in Nebraska a month ago. The typical shelf life for a salad mix is up to 14 days.
There have been more recent illnesses in other states. According to the federal Centers for Disease Control and Prevention, the most recent illness was July 23, but the CDC did not specify a location.
The outbreak of a stomach bug that the two states have linked to bagged salad came as little surprise to food safety experts, who say the process of harvesting, washing and packaging leafy greens provides numerous opportunities for contamination.
Although nutritionists stress the chances of getting sick from vegetables are low compared to the dangers of a diet without them, packaged salads heighten the risk because leaves from several batches often are mixed together.
"The washing and comingling of different batches of lettuce means a hazard that may appear in one field can show up in lots of bags of lettuce because of the common bath," said Caroline Smith DeWaal, director of the food safety program for the Center for Science in the Public Interest, a Washington consumer health advocacy organization.
Last year, the Food and Drug Administration issued more than 20 recalls for packaged salads, romaine lettuce or spinach. Most were due to tests finding listeria or E. coli bacteria, both of which can cause serious illness.
The CDC has estimated that 1 in 6 Americans, or 48 million, get sick from foodborne illnesses each year. About 128,000 are hospitalized, and 3,000 die.
In March the CDC released a study that looked at more than 4,500 food-related outbreaks between 1998 and 2008 and found more illnesses attributed to leafy vegetables -- 22 percent -- than to any other food.