Shredded lettuce is the most likely source of an E. coli outbreak linked to Taco Bell restaurants in the Northeast, federal officials said yesterday as Taco Bell executives tried to reassure customers that it was safe to eat at the fast-food chain.
Investigators have not found E. coli in samples of lettuce, cheese and other ingredients collected from Taco Bell, said David Acheson, a Food and Drug Administration food-safety official. They are focusing on lettuce based entirely on a "case control" study -- a statistical analysis of what Taco Bell patrons who fell ill ate compared with what patrons who didn't get sick consumed.
The analysis, standard in outbreak investigations, also indicated that cheddar cheese and ground beef were possible culprits. But based on the history of outbreaks of food-borne illness associated with the three foods, lettuce is the most likely source, said Christopher Braden, an epidemiologist with the Centers for Disease Control and Prevention.
Investigators and Taco Bell executives said cheese and beef are less likely to be contaminated because the beef is cooked and the cheese is pasteurized.
Seventy percent of Taco Bell's menu items contain lettuce, company President Greg Creed said.
The case control study ruled out green onions as the outbreak's cause.
Taco Bell hasn't served green onions in its 5,800 locations for more than a week, after preliminary tests of samples taken from restaurants where people fell ill came back positive for a deadly strain of E. coli. Investigators said preliminary tests can yield false positives.
Investigators are now tracing the source of the lettuce. Creed said it was grown "in the West" but would not say in which state.
Taco Bell is cooperating with the investigation.
The company buys lettuce that has been washed and shredded and doesn't rinse it at the restaurant, Creed said. California-based Ready Pac supplied produce for all the Taco Bell restaurants in New York, New Jersey, Pennsylvania and Delaware -- the four states where the outbreak is believed to be occurring. The only confirmed victim outside those four states, a South Carolina resident, ate at a Taco Bell in Pennsylvania.
Taco Bell has since switched to another California-based produce supplier, Taylor Farms, and does not plan to pull lettuce from its menu.
As of yesterday, 71 people have been reported infected with E. coli O157:H7 in the outbreak linked to Taco Bell. No one has died. That strain of the bacteria can cause bloody diarrhea and kidney failure.
No new cases of illness have been reported for at least seven days, leading federal officials to say that the outbreak may be nearly over.
"We're fairly confident contaminated product is not being distributed or served," Braden said, citing the short shelf life of the ingredients and Taco Bell's supplier switch.
New Jersey has had the most confirmed cases, with 33. It's followed by New York, with 22, Pennsylvania, 13, Delaware, 2, and South Carolina, 1.
Federal officials said it was unlikely that contaminated lettuce was sent to other parts of the country.
There was also no indication of a connection between the Taco Bell cases and an outbreak of E. coli linked to Taco John's restaurants that sickened about 40 people in Iowa and Minnesota, officials said.