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department of agriculture

A Recent Soft Serve Ice Cream Outbreak and a Look Back at Past Incidents Involving Pathogen Contamination

Ryan Maus · September 6, 2023 ·

A recent outbreak of listeriosis has been linked to Soft Serve On The Go ice cream cups, resulting in 2 illnesses. An investigation by the Pennsylvania Department of Agriculture detected the presence of Listeria monocytogenes in an unopened sample of ice cream taken from a patient’s home. The product isolate was matched to the clinical L. monocytogenes outbreak strain by whole genome sequencing. Five positive samples of finished product obtained from the production facility by the New York State Department of Agriculture and Markets also matched the outbreak strain.

A recall of products distributed nationally is currently ongoing. However, this is not the first outbreak or recall associated with ice cream and many others have occurred as shown in the tables below.

YearLocationPathogenIllnessesDeathsProducer
2022MultistateL. monocytogenes281Big Olaf Creamery
2014WashingtonL. monocytogenes22Snoqualmie Ice Cream
2010-2015MultistateL. monocytogenes103Blue Bell
2005MultistateSalmonella260Cold Stone Creamery
1994MultistateSalmonellaEstimated 224,0000Schwan’s
Past ice cream outbreaks are shown in the following table.
DatePathogenPathogen SourceProducer
07/13/2022L. monocytogenesEnvironmentBig Olaf Creamery, LLC
06/06/2022SalmonellaPeanut ButterTaharka Brothers Ice Cream
02/12/2022L. monocytogenesEnvironmentThe Royal Ice Cream Company, Inc.
04/27/2021L. monocytogenesNot MentionedVelvet Ice Cream
05/14/2020L. monocytogenesNot MentionedRamar Foods
03/17/2020L. monocytogenesEnvironmentWorking Cow Homemade Ice Cream
Recent ice cream recalls due to pathogen contamination are shown in the following table.

Contamination of ice cream products generally occurs after pasteurization, resulting from sources that include the addition of contaminated inclusions (e.g. fruits, nuts, candy, or bakery pieces) to the finished product, contamination from the production environment, and inadequate sanitation of equipment such as filling heads. Freezing ice cream can prevent pathogen outgrowth, but it will not eliminate pathogen presence. Low levels of pathogens causing illness were identified in the 1994 Schwan’s outbreak (Salmonella 0.004-0.46 MPN/g) and 2015 Blue Bell outbreak (L. monocytogenes 3.9-7.1 MPN/g).

Supplier verification programs are critical to evaluate inclusions and reduce the risk associated with them. Inclusions and flavors must be ready-to-eat and any required Process Preventive Controls must have been applied at the supplier, unless the ice cream manufacturer assumes this responsibility.

Sanitation controls are critical to prevent post pasteurization pathogen contamination of finished ready to-eat ice cream products. This is especially true for L. monocytogenes. Cross contamination with L. monocytogenes from the environment is identified in Blue Bell’s 2015 outbreak and numerous recalls. Ice cream processes can be hard to clean, leaving behind nutrients for microbial growth. Listeria can grow,
form biofilms, and persist in harborage sites such as drains leading to cross contamination. Biofilm formation is a constant problem in ice cream producing facilities and requires proper cleaning and sanitizing procedures for their removal and prevention. The effectiveness of sanitation programs are verified by the results attained from a well-designed environmental monitoring program

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