WASHINGTON (AP) - Lettuce was the most likely source of an outbreak of E. coli linked to Taco Bell, federal health officials said Wednesday.
Taco Bell had said contaminated green onions were responsible for the cases of food poisoning - 71 confirmed cases of E. coli in five states, primarily New Jersey, New York and Pennsylvania, as of Wednesday, according to the Centers for Disease Control and Prevention.
Follow-up government testing, however, failed to confirm that.
Interviews with patients and other work led them to believe that lettuce was the probable culprit, health officials said.
"That I would say is the most likely vehicle. I would warn we are not done with the investigation," Dr. Christopher Braden, a medical epidemiologist with the CDC, told reporters.
Investigators had considered cheddar cheese and ground beef as well. They said Taco Bell's menu, which offers various combinations of the same ingredients, made it difficult to pinpoint the source of the contamination.
"That has been the case and is part of the reason it has taken a number of days to identify what might be the contaminated ingredient," Braden said.
The Food and Drug Administration plans to trace the lettuce to its source, said Dr. David Acheson, chief medical officer of the agency's Center for Food Safety and Applied Nutrition. Acheson said that effort could prove difficult because the shredded lettuce was processed in bulk.
The evidence that lettuce was responsible for the illnesses was statistical - it was the item that victims most commonly reported eating.
No Taco Bell food samples, other than white onions from a New York restaurant, have tested positive for E. coli, Acheson said. The E. coli found in the white onion did not match the strain that sickened Taco Bell customers, however.