Lettuce was the most likely source of an outbreak of E. coli linked to Taco Bell, federal health officials said Wednesday.
Officials said the outbreaks appears to be over and that tracing the source of the suspected lettuce could prove difficult because the shredded lettuce was processed in bulk.
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, adding it seems the outbreak has run its course.
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.
He said there is no evidence the Taco Bell outbreak is linked to cases of illnesses linked to Taco John restaurants in Iowa and Minnesota.
Investigators do not know if the suspect Taco Bell lettuce was distributed to other parts of the country. The lack of further cases suggests it was not, Acheson said.
Most E. coli infections are associated with undercooked meat, but increasingly produce is to blame. This fall, an outbreak linked to fresh spinach killed three people and sickened more than 200 others.
“This is a situation that is not tenable,” Braden told reporters, echoing comments from Acheson.
Health officials believe most cases of E. coli contamination originate on the farm, where produce can come into contact with animal feces laden with the bacteria.
E. coli, or Escherichia coli, is a common and ordinarily harmless bacteria found in the guts of cattle and other animals. The E. coli O157:H7 strain can cause abdominal cramps, fever, bloody diarrhea, kidney failure, blindness, paralysis, even death.