WASHINGTON -- An outbreak of salmonella poisoning that sickened at least 400 people in 16 states may have been caused by tanker trucks that carried raw eggs and then ice cream mix, federal officials said yesterday.
The ice cream brand was Schwan's, which recalled the tainted )) mix, the officials said.
An investigation of the outbreak over the past two weeks turned up the explanation, said Dr. David Kessler, the commissioner of the Food and Drug Administration. "We have also identified a practice which presents an unacceptable risk to the public and which must be corrected," he said.
The inquiry was conducted by Dr. Kessler's agency, along with the Centers for Disease Control and Prevention and the Minnesota Department of Health.
Large outbreaks of salmonella poisoning occur every year or two in the United States. The outbreaks, caused by the salmonella bacteria, most often originate with eggs, poultry or undercooked meat and cause diarrhea, abdominal cramps, fever, nausea and vomiting.
So far, more than 400 salmonella cases have been confirmed in the current outbreak, and health officials said that about 10 times that number have probably occurred.
In Maryland, officials confirmed at least three cases of salmonella attributed to Schwan's ice cream.
Dr. Kessler said that raw yolks and whites of unpasteurized eggs were carried in one or more tanker trucks, which were later used to transport pasteurized ice cream mix -- a combination of milk, cream and sugar -- to Schwan's Sales Enterprises in Marshall, Minn.
The mix was then made into ice cream and packaged without additional pasteurization.
Raw eggs are often contaminated with salmonella bacteria. "In this particular situation," Dr. Kessler said, "there was no pasteurization of the ice cream mix after delivery by the tanker truck. We have consulted with industry officials about this practice, and they agree with us that steps need to be taken to prevent this from happening again."
But the problem does not appear to be widespread in the ice cream industry. Virtually all ice cream in the United States is pasteurized just before packaging, but in this case it was pasteurized, then shipped as a mix to another plant. It was then packaged and shipped without being repasteurized.
Dr. Kessler said that two precautions should be taken in the future: Products should be pasteurized just before final packaging and the transportation of food in trucks that have carried raw eggs should be avoided if pasteurization of the food is not possible afterward.
The FDA will increase its surveillance in routine inspections, by taking a closer look at the trucks carrying the food, he said.