Cookie Dough Implicated in E. Coli Outbreak

A multi-state outbreak of food-borne illness has been traced back to an unlikely source: uncooked commercial prepackaged cookie dough. The results of an investigation of a 2009 outbreak of Shiga toxin—producing Escherichia coli (STEC), an important cause of gastrointestinal illness, were published online last week by Clinical Infectious Diseases.

Lead study author Karen P. Neil, MD, of the Centers for Disease Control and Prevention, and her team identified 77 patients from 30 states who were sickened by STEC between March and July 2009. Of these patients, 35 were hospitalized and 10 developed hemolytic-uremic syndrome, though none died. The patients’ median age was 15, 66% were under the age of 19, and 71% were female.

In the past, ground beef, leafy green vegetables, and unpasteurized dairy products have been frequently implicated in STEC outbreaks. But when the usual suspects failed to yield a hypothesis for the source of the infection, open-ended interviews with STEC patients revealed a string of responses including uncooked commercial cookie dough.

In a case-controlled portion of the study, in which STEC patients were compared with age-, sex-, and state-matched controls, 33 of 35 STEC patients (94%) were found to have eaten uncooked commercial prepackaged cookie dough compared with 4 of 36 controls (11%), yielding a matched odds ratio of 41.3. Among the STEC patients who ate uncooked commercial cookie dough, 31 of 33 (94%) reported eating a particular brand, called Brand A by the researchers.

Inspection of the major plant responsible for making Brand A cookie dough did not locate the strain of STEC implicated. However, three nonoutbreak strains of E. coli were isolated from Brand A cookie dough, and the company voluntarily recalled 3.6 million packages of its cookie dough and underwent a product reformulation. Although the researchers found no direct evidence, they suspect that flour used to make the dough was the source of the contamination, as it did not undergo a “kill step” to kill pathogens. As of early 2010, the flour used to make Brand A cookie dough was scheduled to be heat-treated in an effort to prevent future contamination.

The researchers note that this is the first reported E. coli outbreak associated with prepackaged cookie dough. Although the dough’s directions do indicate that it should be cooked before eating, many of those sickened by the dough—adolescent girls in particular—reported purchasing it with no intention of cooking it before eating. As a result, the researchers recommend that commercial cookie dough be made ready to eat and that consumers be educated about the dangers of eating uncooked cookie dough to prevent future infections.