Continued interviewing of foodborne outbreak patients recommended

Cavallaro E. N Engl J Med. 2011;365:601-610.

The nationwide outbreak of Salmonella typhimurium linked to contaminated peanut butter and peanut products between September 2008 and April 2009 led to the recall of 3,918 peanut butter–containing products.

After the recall of products associated with the Peanut Corporation of America’s facility in Georgia, continued case-patient interviews led to the implication of a product from a Texas facility not previously linked to the outbreak, according to Elizabeth Cavallaro, MD, MPH, of the CDC’s Division of Foodborne, Waterborne and Environmental Diseases, and colleagues.

“This outbreak illustrates the challenge posed by ingredient-driven outbreaks,” the researchers wrote. “Many food items made with the same contaminated ingredient may be involved — each with separate distribution channels and consumer bases.”

In collaboration with the FDA and state and local health departments, Cavallaro and colleagues set out to investigate nationwide cases of the outbreak strain that occurred between Sept. 1, 2008, and April 20, 2009. They conducted two case-control studies, one a product trace-back and the other an environmental investigation. A total of 714 patients across 46 states were identified, 23% of whom were hospitalized and 1% died.

The first case-control study included 65 patients and 174 matched controls. Illness was significantly associated with consuming any peanut butter (OR=2.5; 95% CI, 1.3-5.3), peanut butter-containing products (OR=2.2; 95% CI, 1.1-4.7) and was also associated with frozen chicken products (OR=4.6; 95% CI, 1.7 -14.7).

For the second study, illness was associated with consuming peanut butter outside of the home (OR=3.9; 95% CI, 1.6- 10) and two brands of peanut butter crackers (brand A: OR=17.2; 95% CI, 6.9-51.5; brand B: OR=3.6; 95% CI, 1.3-9.8); both cracker brands were made from the same brand of peanut paste (brand X), the researchers wrote.

S. typhimurium was isolated from brand X peanut butter, brand A crackers and 15 other products produced at the Peanut Corporation of America (PCA) facilities in Georgia and Texas.

“The investigation of focal clusters of cases in institutional settings, especially reviewing invoices for foods common among institutions, and rapid trace-back of the suspected food to the point of manufacture provided critical clues in this outbreak,” the researchers wrote. “These findings highlight the need to continue interviewing case patients in an ongoing outbreak, even after one food vehicle has been implicated, and to continually refine hypotheses as more information is collected.”

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