Epidemiology and Infection

Original Papers

Gastrointestinal pathogens

Outbreak of Salmonella enterica serotype I 4,5,12:i:- infections: the challenges of hypothesis generation and microwave cooking

R. K. MODYa1a2 c1, S. MEYERa3, E. TREESa2, P. L. WHITEa4, T. NGUYENa2, R. SOWADSKYa5, O. L. HENAOa2, P. C. LAFONa2, J. AUSTINa2, I. AZZAMa5, P. M. GRIFFINa2, R. V. TAUXEa2, K. SMITHa3 and I. T. WILLIAMSa2

a1 Epidemic Intelligence Service, Division of Applied Sciences, Scientific Education and Professional Development Program Office, Centers for Disease Control and Prevention, Atlanta, GA, USA

a2 Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA, USA

a3 Foodborne, Vectorborne, and Zoonotic Disease Unit, Minnesota Department of Health, St Paul, MN, USA

a4 Applied Epidemiology Staff, Office of Public Health Science, Food Safety and Inspection Service, United States Department of Agriculture, Omaha, NE, USA

a5 Nevada Division of Public and Behavioral Health, Carson City, NV, USA


We investigated an outbreak of 396 Salmonella enterica serotype I 4,5,12:i:- infections to determine the source. After 7 weeks of extensive hypothesis-generation interviews, no refined hypothesis was formed. Nevertheless, a case-control study was initiated. Subsequently, an iterative hypothesis-generation approach used by a single interviewing team identified brand A not-ready-to-eat frozen pot pies as a likely vehicle. The case-control study, modified to assess this new hypothesis, along with product testing indicated that the turkey variety of pot pies was responsible. Review of product labels identified inconsistent language regarding preparation, and the cooking instructions included undefined microwave wattage categories. Surveys found that most patients did not follow the product's cooking instructions and did not know their oven's wattage. The manufacturer voluntarily recalled pot pies and improved the product's cooking instructions. This investigation highlights the value of careful hypothesis-generation and the risks posed by frozen not-ready-to-eat microwavable foods.

(Received November 26 2013)

(Revised June 05 2013)

(Accepted July 03 2013)

(Online publication August 05 2013)

Key words

  • Food safety;
  • foodborne infections;
  • outbreaks;
  • Salmonella enterica


c1 Author for correspondence: Dr R. K. Mody, MD, MPH, Centers for Disease Control and Prevention, Mailstop C-09, 1600 Clifton Road NE, Atlanta, GA 303 33 USA. (Email: rmody@cdc.gov)