With 65 E. coli O157:H7 infections in 29 states appearing to be linked to the consumption of raw Toll House cookie dough, Nestlé's Quality Assurance staff must be scrambling to determine how the pathogen might have sneaked in.
E. coli O157:H7 usually is associated with raw meat, unpasteurized dairy products and raw produce. None of these items can be found on any Toll House cookie dough ingredient list. And none of the cookie dough ingredients ever have been associated until now with E. coli O157:H7 contamination, as far as we can tell.
Unless the pathogen was introduced into Nestlé's production facility by an asymptomatic carrier of the disease – a Typhoid Mary – we would suggest that the most probable source of the contamination is an ingredient.
While we have no inside information on Nestlé's processes or the FDA outbreak investigation, we have figured out one possible scenario. But, first, a little history lesson.
In 1994, nearly 600 people in 41 states suffered from gastroenteritis after consuming Salmonella-contaminated Schwan's ice cream. The contamination was blamed on a "sanitary" bulk tanker truck that had not been properly sanitized after hauling a load of raw liquid egg. The improperly cleaned tanker then was used to transport ice cream mix to Schwan's. The result: Salmonella-contaminated ice cream.
History might be repeating itself in this outbreak. Dairy herds are a major reservoir for E. coli O157:H7, and contamination of raw milk by this pathogen has been documented on several occasions. Bulk tanker trucks haul raw milk from the farm to dairy companies. They also deliver bulk pasteurized egg products to food processors, such as Nestlé.
Perhaps a particular tanker was not sanitized properly between carrying a load of raw milk and a load of bulk pasteurized egg. If so, E. coli O157:H7 may have survived the improper sanitizing treatment, and then contaminated the egg.
This is pure speculation, of course. Nestlé might own a fleet of sanitary tankers that are dedicated to hauling pasteurized egg products. And as of this evening, neither FDA nor Nestlé have reported finding the outbreak strain in any sample of Toll House cookie dough, in the company's production environment, or in any of the ingredients.
But it might have happened that way.