Cold Stone | The International Outbreak Museum

Outbreak: Cold Stone Cake Batter Ice Cream
Product: Cake Batter Ice Cream	Investigation Start Date: 06/29/2005
Location: Multi-state	Etiology: Salmonella Typhimurium
Earliest known case onset date: 05/21/2005	Latest case onset date: 07/04/2005
Confirmed / Presumptive Case Counts: 25 / 0	Positive Samples (Food / Environmental): 2 / 0

Cold Stone Creamery in Seattle, Washington
Bill Keene and Chris Van Beneden outside a Cold Stone Creamery in Seattle, WA
Cold Stone Creamery in Seattle, Washington
Cold Stone Creamery – Seattle, WA: At a store, mix-in ingredients are combined with ice cream to create various customized sundaes and treats.
Melissa Plantega holding a box of cake mix at a Cold Stone Creamery store in Tigard, OR.
Illness onset dates of cases by state of residence: Twenty-five S. Typhimurium isolates of the outbreak PFGE subtype were identified in 10 states. Twenty-four cases in nine states reported consuming Cold Stone Creamery cake batter ice cream prior to onset of illness. The median age of cases was 13 years (range, 2 – 32 years), 58% were female, and illness onsets ranged from May 21 to July 4, 2005. The median incubation period was 4 days (range 1 – 7 days) and four cases were hospitalized.
Traceback results for cake mix used in cake batter ice cream: Tracebacks in Minnesota, Oregon, and Virginia implicated a single lot of cake mix produced on April 14, 2005. No manufacturing anomalies were identified for this lot. Forty-eight percent of this lot shipped to the nine states with cases; 52% shipped to 20 other states. Cake mix and ice cream samples tested by the United States Food and Drug Administration and individual states were negative; however, two cake mix samples were positive for S. Typhimurium of the outbreak PFGE subtype at the University of Georgia Center for Food Safety.
Selected Cold Stone Creamery ice cream flavors and ingredients: The cake batter ice cream recipe called for 2 lbs. of powdered Gold Medal Supermoist Yellow Cake Mix mixed with 2.5 gallons of sweet cream ice cream base. The sweet cream base was used in nearly all Cold Stone Creamery ice cream flavors; therefore, the investigation focused on cake mix.
Cold Stone Creamery – Tigard, OR: A Cold Stone Creamery store posted this sign on their walk-in cooler. Cold Stone Creamery voluntarily recalled cake batter ice cream on July 1, just two days after the outbreak was initially detected.
Gold Medal SuperMoist Yellow Cake Mix: Cake mix pictured here contained flour, spray-dried egg whites, and several low risk components. The implicated lot of cake mix contained two lots of spray-dried egg whites; a 50lb box of one lot was available for testing but was negative for Salmonella. Specific lots of flour used in the cake mix were not determined nor tested. Low levels of contamination could have gone undetected in either ingredient. The difficultly in recovering Salmonella from implicated ice cream and cake mix at several laboratories, and the relatively long incubation period for cases in this outbreak, also suggests low level contamination of the cake mix.
Cake batter mix ingredients.

OUTBREAK SUMMARY:

The vehicle for this outbreak was ice cream made with a contaminated cake mix ingredient. Four patients reported eating cake batter flavor ice cream from two separate outlets of Cold Stone Creamery.

DETAILS:

Salmonella Typhimurium Outbreak Associated with Cake Batter Ice Cream from Cold Stone Creamery

Background
On June 29, 2005, the Minnesota Department of Health identified four Salmonella Typhimurium isolates with a pulsed-field gel electrophoresis (PFGE) subtype that was new to the PulseNet national database. Four patients reported eating cake batter flavor ice cream from two separate outlets of Cold Stone Creamery.

Methods
The PulseNet national database was queried to identify potential cases in other states. A case was defined as infection with an S. Typhimurium isolate that matched the outbreak PFGE pattern, and illness onset since May 2005. All cases were interviewed with a standard questionnaire. State and federal officials conducted a traceback of ice cream ingredients.

Results
We identified 25 cases in nine states (MN, 5; OR, 5; WA, 5; VA, 3; OH, 2; CA, IL, MA, MI, PA, 1 each); 24 reported eating cake batter ice cream from Chain A. The median age of cases was 13years (range, 2–32 years). The median incubation was 4 days (range, 1–7 days). Illness onset dates ranged from May 21 to July 4; four cases were hospitalized. Cold Stone Creamery voluntarily recalled cake batter ice cream on July 1. This flavor’s ingredients included a pasteurized liquid sweet cream base and Gold Medal Super Moist yellow cake mix. The sweet cream base was used in numerous other ice cream flavors, but the cake mix was used only in cake batter ice cream. The cake mix comprised spray-dried egg whites, flour, and several low risk components. Tracebacks in Minnesota, Oregon, and Virginia implicated a single lot of cake mix produced on April 14, 2005. No manufacturing anomalies were identified for this lot; but two cake mix samples yielded the outbreak strain of S. Typhimurium. The Food and Drug Administration warned food retailers that cake mixes and flour are not considered “ready to eat” and should be heat processed before consumption.

Conclusion
The vehicle for this outbreak was ice cream made with a contaminated cake mix ingredient. While the ultimate source of contamination was not confirmed, we recommend a review of the efficacy of spray-drying egg whites as a kill step for Salmonella. Routine and rapid subtyping of bacterial isolates, coupled with a vigorous epidemiological response, is critical to identifying and abating multi-state outbreaks.