FDA made it official yesterday evening. The agency has wrapped up its investigation into Nestlé's Toll House cookie dough manufacturing facility in Danville, Virginia. Raw cookie dough produced in the Danville plant is believed to be responsible for an outbreak of E. coli O157:H7 infections that has sickened 76 people in 31 states. Thirty-five of the victims were hospitalized, 11 with life-threatening hemolytic uremic syndrome.
After an investigation that lasted from June 18th through July 9th, no one is any the wiser as to how at least three different strains of E. coli were able to contaminate the raw cookie dough.
"Three different strains," you ask?
Yes. Three different strains of E. coli have been recovered during the course of this outbreak investigation.
- Strain #1: A common strain of E. coli O157:H7 was isolated from all 76 outbreak victims.
- Strain #2: A different E. coli O157:H7 was isolated by FDA from a retained sample of Toll House raw cookie dough that was analyzed as part of the federal outbreak investigation. The E. coli O157:H7-positive sample was produced on February 10, 2009 (based on package date code #9041)
- Strain #3: E. coli O124 – a completely different strain of toxin-producing E. coli was found in a sample of cookie dough recovered from the home of two Minnesota children who were infected with the outbreak strain.
As Roy Costa pointed out in his guest article on Marler Blog two days ago, "...the finding of more than one E coli O157:H7 strain is clearly indicative of a highly contaminated environment reservoir, and this reservoir is likely in the plant or was during the outbreak."
Or, as I suggested on Saturday, "...a long-standing build-up of contaminants over time."
In an attempt to figure out how this build-up could occur, I've been combing the old inspection reports for the Danville plant that the FDA has posted on its website. The clue may be buried in this excerpt from a 2005 inspection report, which summarizes the cookie dough production process.
"Dry ingredients are weighed out in prep rooms according to recipe specifications. Ingredients are then transported in stainless steel tubs and added to one of several mixers located near the beginning of each production line. Dough is then transferred to a hopper and extruded into either a sheet or a tube (chubs). Dough then passes through a series of cooling tunnels and is either scored or stamped into different shapes depending on the production line. Rework from the cookie dough lines is collected in stainless steel drums and added back into the mixer for a subsequent batch."
"Rework" refers to dough that is left over at the end of a production run - perhaps in the extrusion equipment, in the hoppers, or after trimming away ragged edges. This dough is saved and mixed back in with a subsequent batch – along with any contamination that the reworked dough might have picked up along the way. The Nestlé employee who accompanied the FDA inspector on this particular plant visit dodged the inspector's question as to how long "rework" might be held before being folded into to a new batch of dough.
Subsequent inspection reports do not mention rework; those reports don't describe the production process in any detail. Nor does rework, alone, answer the mystery of where the contamination originated. But it could help explain how the problem may have been perpetuated.
Nestlé has completely dismantled, cleaned and disinfected its raw cookie dough production lines. The company also has changed to new suppliers for its main ingredients, and is phasing production back in on a limited basis.
FDA has remained close-mouthed on any investigations it may have carried out of Nestlé's ingredient suppliers, or whether any of these investigations are still in progress. But from the tone of the most recent FDA update, the agency will be adding this particular outbreak to its "Unsolved Mysteries" file.