On June 30, 2005 the Minnesota Department of Health notified the federal Centers for Disease Control and Prevention (CDC) that four cases of Salmonella Typhimurium (S. Typhimurium) with an indistinguishable Pulsed Field Gel Electrophoresis (PFGE) subtype (CDC PulseNet pattern JPXX01.1173) had been identified. This subtype was new to the PulseNet database. Illness onset dates ranged from June 1 to June 9. The only common exposure among the four ill individuals was that all had eaten at one of two Cold Stone Creamery stores. All cases had eaten cake batter flavor ice cream in the week before onset of symptoms.

The following day (July 1) an electronic posting describing the outbreak was distributed to state health departments via the CDC sponsored “Foodborne-Outbreak” listserve. More cases with PulseNet pattern JPXX01.1173 were identified in Ohio (n=2), Oregon (n=3) and Washington (n=5). Six of these patients had been interviewed, and all six reported eating ice cream purchased at a Cold Stone Creamery (CSC) store in the week prior to becoming ill. Five of the six patients interviewed could recall the flavor of ice cream they consumed. All five had eaten cake batter mix ice cream. The epidemiologic evidence implicating CSC cake batter mix ice cream as the source of illness was so compelling that health investigators notified Cold Stone Creamery headquarters that a nationwide foodborne outbreak associated with a CSC product was occurring.
Ironically, July 1 also marked the start of National Ice Cream month. To celebrate, Cold Stone Creamery planned to offer free samples at each of its more than 1080 stores located nationwide on July 2. State and federal agencies scrambled to issue a health press release advising CSC customers that consumers of the company’s cake batter mix ice cream should watch for gastrointestinal symptoms and contact their local health department if they were ill. See Attachment No. 1, Cold Stone Creamery and Food and Drug Administration Issued a Nationwide Alert on Possible Health Risk Associated With “Cake Batter” Ice Cream. Any of the implicated ice cream that had been purchased for home consumption needed to be discarded and the store contacted for a refund. That afternoon company officials voluntarily removed all cake batter products from all of its stores throughout the country.
Local, state, and federal health agencies worked collaboratively to identify potential outbreak-associated cases. Oregon Health Division (OHD) and Minnesota Department of Health (MDOH) epidemiologists led the investigation. When a case of S. Typhimurium was reported, health investigators asked about possible ice cream exposure. A standardized questionnaire was administered to all S. Typhimurium cases who reported eating at a Cold Stone Creamery. Individuals were asked about date of purchase, store location, flavor, mix-ins, and amount consumed.
Over the next few days new outbreak associated cases were identified through case interview and confirmed by PFGE subtyping. In addition to cases reported in Ohio, Washington, and Oregon, reports of cases came from Michigan, Massachusetts, Virginia, and Illinois. In spite of having more than 250 CSC stores in California, only one person in California was laboratory confirmed with S. Typhimurium and linked to the outbreak.
MDOH epidemiologists and FDA staff worked to obtain more information on the ice cream. Basic ingredients of the cake batter ice cream consisted of cake batter mix made by General Mills and a pasteurized liquid sweet cream base manufactured by Kohler Mix Specialties, Inc. The sweet cream base was used in numerous other ice cream flavors, but the cake mix was used only in cake batter ice cream. Investigators focused their attention on the powered cake mix. General Mills contact, Sarah Geisert, provided a list of ingredients for the cake batter mix which included spray-dried egg whites and flour, items that have previously been shown to be contaminated with Salmonella. 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; Salmonella test results for cake mix samples are still pending. General Mills asserted that Cold Stone Creamery did not use the cake mix appropriately, maintaining that it was not intended to be used in unbaked form.
The FDA concurred and on August 9, 2005 the agency issued a bulletin to the food service industry, “Regarding Cake Batter Ice Cream and Similar Products.” See August 9 FDA Bulletin, Attachment No. 2, It read:
“The U.S. Food and Drug Administration (FDA) is informing the retail and food service industries that incorporating an ingredient that is intended to be cooked into a ready-to-eat food that will not be cooked or otherwise treated to eliminate microorganisms of public health concern can pose a serious food safety risk. A recent multi-state outbreak of Salmonella Typhimurium has been associated with consumption of “cake batter” ice cream.”
The FDA repeated their warning.
“This Cake Batter Ice Cream was prepared in food service establishments. The preparation involved adding a dry cake mix to a pasteurized sweet cream base and the combination did not undergo additional processing prior to freezing. Dry cake mix is a product that has been designed to be rehydrated and then cooked. Dry cake mix should not be considered a ready-to-eat food because it has not been processed to ensure that pathogens have been destroyed or reduced in numbers to an acceptable level. Ready-to-eat foods are typically processed to ensure that they are safe to consume without further cooking. Similar products, such as “cookie dough” ice creams and “cake mix” milk shakes, could also pose a serious food safety risk if they are prepared with ingredients that are intended to be cooked.”
The Oregon Health Division served as the repository for completed case-patient questionnaires and compiled the data. Twenty-five cases in nine states (MN, OR, WA, VA, OH, CA, IL, MA, MI, and PA) were identified; 24 reported eating cake batter ice cream from Cold Stone Creamery. The median age of cases was 14 years (range, 2-32 years). The median incubation was 3.5 days (range, 1-7 days). Illness onset dates ranged from May 24 to July 4. Four cases were hospitalized. See Attachment No. 3, “Salmonella Typhimurium Outbreak Associated with Cake Batter Ice Cream from Nationwide Ice Cream Chain”, abstract submitted for consideration to the International Conference on Emerging Infectious Diseases. The final outbreak report is still pending.
This was not the first outbreak of Salmonella associated with consumption of commercially produced ice cream. One of the largest foodborne outbreaks ever reported was linked to ice cream. In September 1994 the Minnesota Department of Health investigated a cluster of Salmonella enteriditis. A case control study implicated a nationally distributed brand of ice cream distributed by Schwan Food Company. Health investigators estimated that more than 224,000 persons nationwide developed S. enteritidis as a result of consuming Schwan ice cream. Ice cream premix was contaminated when it was transported in tanker trailers that had previously carried nonpasteurized liquid eggs containing S. enteriditis.
Homemade ice cream has frequently been linked to infection with Salmonella. During the period 1966 to 1976, 22 outbreaks with 292 cases of salmonellosis associated with the consumption of homemade ice cream were reported to the CDC. S. typhimurium accounted for 45% of the outbreaks. The source of eggs used was known in 13 outbreaks, and all were from ungraded farm- or home-produced eggs. In all instances, the ice-cream custard had not been cooked before freezing. Between 1996 and 2000, the CDC reported 17 outbreaks resulted in illness in more than 500 people which were associated with homemade ice cream.