THE NEW ENGLAND JOURNAL OF MEDICINE

Salmonella Typhimurium Infections Associated with Peanut Products

Elizabeth Cavallaro, M.D., M.P.H., Kashmira Date, M.D., M.P.H., Carlota Medus, Ph.D., M.P.H., Stephanie Meyer, M.P.H., Benjamin Miller, M.P.H., Clara Kim, Ph.D., Scott Nowicki, M.P.H., Shaun Cosgrove, B.S., David Sweat, M.P.H., Quyen Phan, M.P.H., James Flint, M.P.H., Elizabeth R. Daly, M.P.H., Jennifer Adams, B.S., Eija Hyytia-Trees, Ph.D., D.V.M., Peter Gerner-Smidt, M.D., D.M.S., Robert M. Hoekstra, Ph.D., Colin Schwensohn, M.P.H., Adam Langer, D.V.M., M.P.H., Samir V. Sodha, M.D., M.P.H., Michael C. Rogers, M.S., Frederick J. Angulo, D.V.M., Ph.D., Robert V. Tauxe, M.D., M.P.H., Ian T. Williams, Ph.D., and Casey Barton Behravesh, D.V.M., Dr.P.H. for the Salmonella Typhimurium Outbreak Investigation Team

N Engl J Med 2011; 365:601-610August 18, 2011

Background

Contaminated food ingredients can affect multiple products, each distributed through various channels and consumed in multiple settings. Beginning in November 2008, we investigated a nationwide outbreak of salmonella infections.

Methods

A case was defined as laboratory-confirmed infection with the outbreak strain of Salmonella Typhimurium occurring between September 1, 2008, and April 20, 2009. We conducted two case–control studies, product “trace-back,” and environmental investigations.

Results

Among 714 case patients identified in 46 states, 166 (23%) were hospitalized and 9 (1%) died. In study 1, illness was associated with eating any peanut butter (matched odds ratio, 2.5; 95% confidence interval [CI], 1.3 to 5.3), peanut butter–containing products (matched odds ratio, 2.2; 95% CI, 1.1 to 4.7), and frozen chicken products (matched odds ratio, 4.6; 95% CI, 1.7 to 14.7). Investigations of focal clusters and single cases associated with nine institutions identified a single institutional brand of peanut butter (here called brand X) distributed to all facilities. In study 2, illness was associated with eating peanut butter outside the home (matched odds ratio, 3.9; 95% CI, 1.6 to 10.0) and two brands of peanut butter crackers (brand A: matched odds ratio, 17.2; 95% CI, 6.9 to 51.5; brand B: matched odds ratio, 3.6; 95% CI, 1.3 to 9.8). Both cracker brands were made from brand X peanut paste. The outbreak strain was isolated from brand X peanut butter, brand A crackers, and 15 other products. A total of 3918 peanut butter–containing products were recalled between January 10 and April 29, 2009.

Conclusions

Contaminated peanut butter and peanut products caused a nationwide salmonellosis outbreak. Ingredient-driven outbreaks are challenging to detect and may lead to widespread contamination of numerous food products.
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