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Cold Stone

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


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.


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

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.

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.

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.

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.

Jack-in-the-Box Hamburgers

Outbreak: Jack In The Box Hamburgers 
Product: HamburgersInvestigation Start Date: 01/12/1993
Location: Multi-State OutbreakEtiology: E. coli O157
Earliest known case onset date: 11/18/1992Latest case onset date: 02/21/1993
Confirmed / Presumptive Case Counts: 503 / 229Positive Samples (Food / Environmental / Water): 0 / 0 / 0
Hospitalizations: 151Deaths: 3

This was the largest outbreak of E. coli O157 infections ever documented in the United States, and it injected this pathogen—and threats to food safety in general—into popular consciousness.


On January 12, 1993, a pediatric gastroenterologist notified the Washington State Department of Health (WSDOH) of an increase in emergency department visits for bloody diarrhea and the hospitalization of three children with hemolytic uremic syndrome.

Hypothesis-generating interviews suggested exposure at Jack In The Box restaurants, and in a swiftly conducted matched case-control study WSDOH confirmed association of illness with Jack-in-the-Box hamburgers.

After news of the Seattle outbreak broke, clusters of bloody diarrhea and lab-confirmed E. coli O157 infections were soon recognized as associated with Jack In The Box hamburgers in California, Nevada and Idaho — an association confirmed by molecular testing by the newly developed Pulsed-Field Gel Electrophoresis (PFGE)method.

Observation of cooking methods revealed that hamburgers did not consistently reach internal temperatures lethal for E. coli. Product trace-backs implicated selected lots of hamburgers (picture); culture of uncooked hamburger patties corroborated the epidemiologic findings. (1)

Several pivotal public-health initiatives were undertaken in this outbreak’s wake:

1. At the time of the outbreak, E. coli O157 infection was reportable in only 12 states. By the end of 1994, 33 states had made it reportable, and by the end of 1996, it was reportable in all but 6 states.

2. The outbreak “broke” the weekend of Bill Clinton’s first Presidential inauguration, and it was one of the first exigencies that faced the new administration. Agriculture Secretary Mike Espy proposed sweeping changes to existing regulations regarding beef production, which had required only visual inspection of beef-processing operations. Under the new rules, USDA began testing samples of raw ground beef in 1994 for E. coli O157, which was declared an “adulterant,” indicating a zero-tolerance policy for its presence even in uncooked beef; and in 1996 required the risk-reduction system known as “Hazard Analysis & Critical Control Points” (HACCP) in meat-processing establishments.

3. A renewed emphasis on foodborne illness was undertaken at CDC. In 1995, “FoodNet” was initiated to capture detailed data regarding foodborne illnesses systematically and to conduct special studies into their sources. Today, food safety has public health prominence as one of CDC’s “Winnable Battles.”

4. The Jack In The Box outbreak was the first major use of PFGE — a new DNA typing technique that could explore relatedness of bacterial isolates. CDC trained and funded state health departments to test bacterial isolates routinely using this method and to report to a centralized system, where widespread but low-level outbreaks could be detected. Today, this “PulseNet” system can be credited with detecting a substantial fraction of recognized foodborne outbreaks.

References: 1. Tuttle et al. “Lessons from a large outbreak of Escherichia coli O157:H7 infections: insights into the infectious dose and method of widespread contamination of hamburger patties.”