THURSDAY, Dec. 14, 2006 (HealthDay News) -- U.S. health officials late Thursday declared the E. coli outbreak linked to Taco Bell restaurants in the Northeast to be over, even as the investigation into suspect lettuce continued.
In their declaration, officials at the U.S. Centers for Disease Control and Prevention also said, "Based on a number of factors, iceberg lettuce is considered overall to be the single most likely source of the outbreak at this time."
Tests on green onions, initially thought to be the cause of the bacterial outbreak that sickened at least 71 people in five states, had proven negative, health officials said earlier.
"We have identified several ingredients that may be associated with the outbreak. These include lettuce, ground beef and cheddar cheese," Dr. Christopher Braden, a medical epidemiologist at the U.S. Centers for Disease Control and Prevention, said during a teleconference late Wednesday. "The most likely food vehicle is lettuce. But we are still looking at other food items."
Dr. David Acheson, chief medical officer at the U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition, said it was too early to speculate where the lettuce -- if it is proven to be the source of the contamination -- was grown.
"To date, no food samples have come up with E. coli that matches the outbreak," Acheson said. "The primary focus is on lettuce, but we are also looking at cheese."
The FDA hopes to trace the lettuce to its source, but officials conceded that could be tough because the lettuce was shredded and processed in bulk.
Taco Bell said after the news conference that a CDC analysis showed a "statistical probability" that lettuce was the source of contamination, after the agency conducted interviews with those who have become ill. Lettuce is served in approximately 70 percent of all Taco Bell menu items. The lettuce supplied to Taco Bell restaurants in New York, New Jersey, Pennsylvania and Delaware was grown by various farmers and shipped to the company's former produce supplier, the company said in a prepared statement.
The outbreak also appears to be winding down, the FDA officials added, although there are people who still may be confirmed with the illness in coming days.
"These numbers may increase in the next few days. However, we are seeing a decline in cases," Braden said.
Acheson added that there was "no indication that the Taco Bell outbreak has anything to do with the Taco John E. coli outbreak in Minnesota and Iowa."
Almost three dozen people have fallen ill in recent days with symptoms consistent with E. coli infection after eating at a Taco John's restaurant in Cedar Falls, Iowa.
Authorities are also investigating reports that at least 14 other people became ill after eating at Taco John restaurants in Albert Lea and Austin, both in Minnesota. Both Taco Bell and Taco John are separate companies, with no affiliation.
Last week, officials from the CDC and the FDA were concentrating on green onions, also called scallions, as the likely source of the Taco Bell outbreak, but laboratory tests failed to prove such a link.
But the company didn't take any chances. Taco Bell on Saturday announced it had removed all green onions from its 5,800 restaurants nationwide.
"We're focused on working with the authorities to find the root cause," Rob Poetsch, a spokesman for Yum! Foods, which owns Taco Bell, said at the time.
Acheson said earlier this week that testing of a sample of white onions from a Taco Bell on New York's Long Island by county health officials found the produce was contaminated with E. coli, but that the strain was not the same as the one identified in the wider outbreak.
"It doesn't match the outbreak strain or any strain associated with the illnesses," Acheson said.
As of Wednesday evening, the CDC was reporting 71 confirmed cases of E. coli infection in five states. New Jersey had 33 confirmed cases; New York had 22; Pennsylvania had 13, Delaware had two, and South Carolina had one. The South Carolina patient ate at a Taco Bell in Pennsylvania, according to the CDC.
Of the confirmed cases on the CDC list, 76 percent of the victims required hospitalization and 12 percent developed a form of kidney failure called hemolytic-uremic syndrome, the agency said.
In a statement released this week, Taco Bell said independent laboratory test results of more than 300 samples of all the ingredients served in Taco Bell restaurants concluded that no ingredient contained the E. coli bacteria 0157:H7.
"Out of an abundance of caution, we switched our produce supplier for all of our produce, including white onions, for New York, New Jersey, Pennsylvania and Delaware. Since the independent scientific laboratory tests on all of our ingredients have concluded negative for E. coli, we have no information regarding any Taco Bell ingredient linked to this outbreak," said Greg Creed, president of Taco Bell Corp.
The E. coli outbreak was the third food-borne illness to plague U.S. consumers in recent months. In September, an outbreak of E. coli-contaminated spinach sickened 199 people in 26 states and Canada and left three dead.
Also in September, an outbreak of salmonella was traced to tomatoes served in restaurants. The outbreak sickened 183 people in 21 states, as well as two people in Canada.
According to the CDC, E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless, this one produces a powerful toxin that can cause severe illness.
The germ is found on most cattle farms, and meat can become contaminated during the slaughter process. Other possible sources of food-borne infection are lettuce, sprouts, spinach, salami, unpasteurized milk and juice.
Infection with E. coli O157:H7 often causes severe bloody diarrhea and abdominal cramps. Sometimes, it causes non-bloody diarrhea or no symptoms. The illness typically clears up within five to 10 days, according to the CDC.
For more on the latest E. coli outbreak, visit the U.S. Centers for Disease Control and Prevention.