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

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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

IAFP 2023 – Intentional Adulteration (IA) Rule – Update

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The IAFP Food Defense PDG heard a regulatory update on the
Intentional Adulteration (IA) Rule at the annual meeting in Toronto.
Colin Barthel, a policy analyst at FDA (FDECS, OAO, CFSAN) discussed the status of ongoing Food Defense Plan Quick Checks, the Food Defense Plan Builder version 2.0, and what’s next for future full Food Defense Plan inspections.


Food Defense Plan Quick Checks have been occurring during Food Safety (Preventive Controls) inspections conducted by FDA since October 2020. Inspectors assess if a firm is subject to the IA Rule and conduct a visual inspection for presence or absence of a Food Defense Plan. Currently, about 1,000 Quick Checks have been conducted with 70% occurring at domestic facilities and 30% at foreign facilities. Sixty percent of facilities have used the Key Activity Types to conduct their vulnerability assessment while 5% of facilities did not do a vulnerability assessment or have a Food Defense Plan in place.

The Food Defense Plan Builder version 2.0 is a user-friendly tool available to help owners and operators of a food facility to develop a food defense plan that is specific to their facility and meet the requirements of the IA Rule. It has been downloaded 11,489 times. This is more than the estimated 10,000 registered
domestic facilities revealing that many others are also finding this tool useful. The FDA is accepting feedback on the Food Defense Plan Builder version 2.0 for use in updating a future version.


Next steps for FDA involve developing a Food Defense Inspection Team to begin conducting full Food Defense Plan inspections in the next fiscal year. A supervisor for the team was hired and five investigators are to be trained over the next 12 months to conduct full inspections. The FDA identified 25-30 factors that will be used to identify facilities that will be prioritized for full inspection. Currently, all FDA inspections are transitioning to be unannounced. Violations occurring in full Food Defense Plan inspections will be handled as they are for Preventive Controls inspections; they will begin with a FDA form 482 and end with a FDA form 483 being issued.

IA Rule regulatory requirements for covered facilities include the need for a Food Defense Plan. Components of the Plan are a vulnerability assessment; implemented mitigation strategies; documented monitoring activities, corrective actions, and verification procedures. Training and recordkeeping are also requirements. More information is available on FDA’s website. The Food Defense Plan is overseen by a Food Defense Qualified Individual. Training developed to align with regulatory requirements is available from FSPCA.


Resources to assist industry comply with the IA Rule include:

IAFP 2023 – Symposium Discusses Establishing Microbiological Performance Standards for Food Safety

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A symposium at IAFP 2023 (S36), “Establishing Microbiological Performance Standards for Food Safety” discussed how industry establishes performance standards for a broad category of food then validates them to meet regulatory requirements. Performance standards are the specific pathogen reduction levels that must be attained during processing to ensure that proper food safety has been achieved. These can be established based on current available scientific literature, scientific studies performed by the company, regulatory requirements, or by using
risk-based pathogen modeling. Validation then demonstrates that the performance standard can be met during routine processing of food.

Stephanie Nguyen, Principal Microbiologist at ConAgra Foods, discussed considerations for designing performance standards for ready-to-eat (RTE) meat and plant proteins, canned foods, and frozen vegetables. For cell cultured meat, FDA regulates the cell collection, banking, growth and differentiation of the cells, then oversight is transitioned to USDA-FSIS at the harvesting stage. These products need to meet USDA pathogen log reductions set forth for meat products from which the original cells originated from (i.e. FSIS Appendix A). Plant based protein products

should attain a minimum 5-log pathogen reduction, the performance standard generally considered acceptable for FDA regulated products in the absence of other readily available performance standards. Performance standards for low acid canned foods are outlined in 21 CFR Part 113 and consist of applying a 12-log reduction in spores while acidified canned food guidance is outlined in 21 CFR part 114. Frozen vegetables are unique in that they are non RTE, therefore validated cooking instructions can provide the consumer necessary requirements to attain a 5-log reduction in pathogen hazards.

Rico Suhalim, Process Authority at PepsiCo, discussed considerations for designing performance standards for juices, sweet and salty snacks, including low-water activity (aw) foods. For acidified juices, HACCP guidance is available from FDA. Thermal processing to meet a minimum 5-log pathogen reduction for acidified foods pH 4.1–4.6 is described by Breidt et al., 2014. For low aw snacks, challenge studies and process validations are generally conducted to meet a 5-log pathogen reduction. It is important to control microbial load with incoming raw ingredients and understand that thermal processes designed for one food matrix may not be appropriate for another (i.e. kibble ≠ meat).

Aaron Uesugi, Principal Scientist at Mondelez, discussed considerations for designing performance standards for bakery and confectionery products. Processors should consider whether they are baking or drying to assess microbial end product risks appropriately. Bakery products can generally be validated for a 5-log pathogen reduction. However low moisture raw ingredients placed on top of the raw dough, such as sesame seeds, should be assessed to make sure they also achieve a 5-log pathogen reduction during the baking process. It is also important to control microbial hazards that may be introduced post process. For example, chocolate can’t be heated to reduce Salmonella risk, roasting the cocoa bean is the only 5- log pathogen kill step, thus sanitation preventive controls verified by an environmental monitoring program are critical to the production of safe product.

A recording of the symposium is available from IAFP and a 2022 publication by one of the presenters provides more information on this topic. Deibel Laboratories has process authorities available to design and conduct challenge studies and validations to meet regulatory safety requirements for your food products.

L. monocytogenes Contaminated Pineapple Leads to Recall of Frozen Fruit Products

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A recall of frozen fruit products distributed by major retailers was recently initiated due to contamination of pineapple with Listeria monocytogenes. Little information is provided on where the contamination was detected or how it occurred. Pineapple generally has a low pH below 4.0 that would inhibit Listeria outgrowth. However, pineapple has been involved in outbreaks and pathogens can persist in low pH products and cause illness. The following provides a review of past pineapple incidents and findings.

Pineapple is commonly started in fields by vegetative propagation (i.e. using cuttings from mother plants) producing fruit in 15-22 months. Greater than an inch of water is required each week for growth. The pineapple fruits are harvested by hand and transported to a factory where they are washed, peeled, and cut into pieces prior to final processing into fresh, frozen, or canned products.

While pineapple has not been implicated in outbreaks of L. monocytogenes, it has been associated with outbreaks resulting from enterohemorrhagic E. coli O11:H43 in 1994, Salmonella Weltevreden in 1996, and Salmonella Javiana in 2020. The 1996 outbreak resulted from contaminated industrial water used to wash the fresh produce. A warning letter issued in response to the 2020 outbreak investigation found the following violations:

  • The hazard analysis did not identify and evaluate environmental pathogens to determine whether they are a hazard requiring a preventive control (e.g., sanitation controls).
  • Lapses in GMPs and Sanitation
    • Cleaning did not occur prior to sanitizing. o Monitoring, verification, and record keeping were not implemented.
    • Handwashing SOPs were not implemented correctly
    • Environmental monitoring procedures to verify sanitation controls were not written or implemented.
  • Supply-chain controls were not implemented
    • Reasonably foreseeable hazards such as Salmonella, L. monocytogenes, and pathogenic E. coli were not assessed for the raw agricultural commodities.
    • The washing step was not an adequate preventive control for pathogens if controls are not also in place by the supplier to minimize pathogen contamination.

Listeria monocytogenes is ubiquitous in nature and a natural part of the pineapple growing environment that can transfer to downstream products through environmental contamination during further processing. Once the fruit is manipulated by peeling, cutting, etc. it falls under the Preventive Controls for Human Food Rule and FDA considers L. monocytogenes a pathogen hazard that requires control.

If there is a lapse in control, pathogens such as E. coli O157:H7, Salmonella, and L. monocytogenes have shown the ability to persist in low pH products stored at freezing temperature for long periods of time, potentially resulting in illness if consumed

FDA Releases Findings on RTE Dips and Spreads

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In 2021, the U.S. Food and Drug Administration (FDA) conducted a routine assignment to collect domestic multi-commodity ready-to-eat (RTE) refrigerated dips and spreads to test for Listeria monocytogenes and Salmonella spp. The agency’s goal in conducting this assignment was to determine the prevalence of these pathogens in RTE dips and spreads and remove adulterated products from the market, when possible.

The assignment, which ran from March 2021 to January 2022, found that four out of the 747 samples tested were contaminated with Salmonella or L. monocytogenes. Ready-to-eat foods can become contaminated with environmental pathogens from harborage sites in the food manufacturing environment or process. Cross-contamination from ingredients can also occur.   Additionally, dips and spreads often have a pH and water activity that favor bacterial survival and outgrowth.  Consumers typically eat these dips and spreads without a ‘kill step,’ such as cooking, to reduce or eliminate any pathogenic bacteria that may be present. As such, dips and spreads contaminated with L. monocytogenes or Salmonella can present a significant public health risk. Ready-to-eat dips such as hummus and cheese spreads have been associated with multiple recalls over the past few years. The FDA’s assignment was initiated due to five recalls of hummus products and six recalls of multi-commodity dips found to be contaminated with L. monocytogenes or Salmonella from FY2017 through FY2020.

During the sampling assignment, the FDA identified Salmonella Havana in a sample of hummus from a retail establishment in California.  The FDA notified the manufacturer of the hummus and a recall was initiated.  The FDA conducted a follow-up inspection at the manufacturer of the contaminated product to evaluate the firm’s manufacturing operations and collect environmental samples. The FDA found that the firm did not establish and implement adequate written procedures for monitoring sanitation control procedures (i.e., cleanliness of food-contact surfaces). The environmental samples collected at the follow-up inspection did not yield any positive pathogens, however, the agency still issued a warning letter after the follow-up inspection.  After taking corrective actions, the firm was unable to identify a root cause for the Salmonella Havana contamination in the hummus.

The FDA identified L. monocytogenes in three samples from a retail establishment in Colorado and the agency notified the firm where the positive samples were manufactured. All three of the samples contaminated with L. monocytogenes were produced by the same manufacturer. Upon notification of the contaminated samples, the firm recalled and destroyed the products associated with the positive findings. The agency issued a Consumer Advisory in conjunction with the firm’s recall.

The agency conducted a follow-up inspection at the manufacturer of the three contaminated products. The follow-up inspection sought to evaluate the firm’s manufacturing operations and collect environmental samples to determine potential sources and routes of contamination. The FDA found L. monocytogenes in 23 swabs collected within the production environment, including samples collected from food contact surfaces. WGS analysis was conducted on the L. monocytogenes isolates obtained from both the retail product samples and the inspection environmental samples. The isolates were a genomic match to each other.

The FDA’s follow-up inspection determined the firm’s employees were not trained in food safety or hygiene practices and found multiple instances of deficient sanitation practices related to equipment, utensils, and employees. The agency determined that the firm did not respond appropriately to the positive samples identified in the sampling assignment and had not addressed objectionable conditions observed by the FDA during a previous 2020 inspection.  The firm went out of business at the end of June 2021.

Underscored in the FDA’s report is the necessity for manufacturing firms to have good manufacturing practices in place, as well as a proper environmental monitoring program and adequate training for its staff as part of their standard business operating procedures.

Deibel Laboratories has years of experience in conducting shelf-life studies, formulation reviews, and validations for refrigerated dips and spreads.  Our staff of industry experts is ready to assist you in assuring that your manufacturing processes and facilities comply with the stringent food safety standards required by the FDA and USDA.  With a complete suite of accredited pathogen testing methods and the testing capacity of 15 laboratories strategically placed throughout North America, Deibel Laboratories is your one-stop for assuring food safety compliance.

Contact us at Sales@DeibelLabs.com for more information about a laboratory near you. Visit us at https://deibellabs.com/services/deibel-guardianemp/ to learn more about our environmental monitoring program, Deibel GuardianEMPsm. Link to FDA findings: FY21-22 Sample Collection and Analysis of Domestic Refrigerated RTE Dips and Spreads | FDA