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IAFP 2023 – Symposium Discusses the Investigation of Ambiguous Outbreaks

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A symposium at IAFP 2023 (S64), “Investigating Ambiguous Outbreaks and Adverse Events” sponsored by the Institute for the Advancement of Food and Nutrition Science (IAFNS) Food Microbiology Committee discussed the topic of “ambiguous outbreaks,” those outbreaks of foodborne illness for which definitive sources and/or pathogens targets are not known.

The FDA will issue a public health advisory for outbreak investigations that result in specific, actionable steps for consumers to take to protect themselves. However, some outbreak and adverse event investigations may not conclusively identify a source or reveal any contributing factors. Actionable steps for consumers are not available. FDA maintains a list of outbreak and adverse event (self-reported) investigations managed by their CORE Response teams. Although an investigation may reveal a particular product or product category as a possible source of illness, the FDA will not publicly name a specific product until there is sufficient epidemiological evidence to implicate that product as a cause of illness or an adverse event.

Many investigations do not identify a pathogen or food vehicle responsible for an outbreak or self-reported illnesses in an adverse event despite extensive testing for numerous potential microbial and chemical adulterants. What learnings can be taken from these investigations that could improve resolution and contribute to an improved prevention strategy? This symposium delved into the question. A recording of the symposium will be available from IAFP.

Speakers discussed improved investigational approaches and tools, the use of Root Cause investigation and analysis to uncover factors leading to attribution, improved outbreak communication strategies for reaching consumers and industry, and new areas of research.

Ambiguous outbreaks can be grouped into one or more of the following categories: outbreaks with a known source and unknown agent, a known agent and unknown source, or an unknown agent and unknown source. Dr. Craig Hedberg, University of Minnesota, discussed improved investigational tools to detect and identify a causative agent such as culture independent diagnostic tests (CIDT) and whole genome sequencing. He also reviewed advances in epidemiological and environmental assessments that improve the chances of making connections between an illness and the source when studying outbreaks for which definitive sources and/or pathogens targets are not known.

Dr. Tim Jackson, FDA, reviewed reasons why the root cause of an outbreak is often ambiguous. Investigations into outbreaks are usually retrospective, analytical testing is statistically limited and often inconclusive, and some foods with short shelf lives may not be available for analysis. Additionally, there may be limited tools for analysis of some causative agents. With multi-component or assembled products, processes and supply chains may be complex with a variety of growers/suppliers, manufacturers, retailers, and distributors. Accurate and precise traceability programs are essential to the evaluation of underlying causes. Dr. Jackson discussed the tools available for root cause investigation and analysis and provided examples of how they have been used in the resolution of outbreaks.


Michael Vasser, CDC, examined the impact of reoccurring, emerging, and persisting (REP) strains on ambiguous outbreaks. Some enteric bacterial strains cause acute outbreaks linked to specific sources. Other strains that are closely related by whole genome sequencing, referred to as REP strains, can reoccur and periodically cause acute outbreaks. They can also emerge and increase in frequency or persist and cause illnesses over periods of months or years, despite investigation and prevention efforts. They do not present as typical acute outbreaks. While illnesses caused by REP strains may be associated with a common reservoir or source, the linkage is often inferred but not proven. Mr. Vasser commented that, in fact, most illnesses reported through PulseNet are not linked to a source (90% of isolates do not have an assigned cluster code). REP strains could actually be the cause of a larger fraction of illnesses than
typical outbreaks. Investigation of REP strains will create opportunities to characterize new sources of enteric disease and develop novel prevention approaches.


Mitzi Baum, STOP Foodborne Illness, discussed the critical need for improved communication channels to the public and industry when outbreaks occur. Stop Foodborne Illness is a non-profit public health organization in the United States dedicated to the prevention of illness and death from foodborne pathogens. The organization was founded in 1993 following an E. coli O157:H7 outbreak in California and the Pacific Northwest. While ambiguity in investigations does occur, it is essential that public health officials provide relatable and actionable information to consumers in these circumstances.



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.

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

The Eight Most Important Recommendations for Controlling Listeria monocytogenes in Retail Delicatessens

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The USDA Food Safety and Inspection Service (FSIS) recently published a guidance document that provides recommendations that retailers can use in delicatessens to control L. monocytogenes contamination of ready-to-eat (RTE) meat and poultry products. This 2023 document is a revised version of the 2015 FSIS Best Practices Guidance for Controlling Listeria monocytogenes (Lm) in Retail Delicatessens. It reflects the FSIS’s current thinking on this topic and is not a regulation. While focused on small firms, the recommendations made will be useful for all meat and poultry retail firms.


Recommendations are based on the joint FSIS, Food and Drug Administration (FDA), and Centers for Disease Control and Prevention (CDC) 2013 Listeria monocytogenes in Retail Delicatessens Interagency Risk Assessment. The assessment summarizes the risks posed by L. monocytogenes from the consumption of RTE foods commonly prepared and sold in retail delis.

The guidance addresses:

  • Actions retailers can take in the delicatessen (deli) area to decrease the potential for
    L. monocytogenes growth and cross-contamination.
  • Steps retailers can take to help ensure that deli products are maintained under sanitary conditions
    that do not allow L. monocytogenes adulteration of the product.
  • Information from the U.S. Food and Drug Administration’s (FDA) Food Code, scientific literature,
    other guidance documents, and lessons learned from meat and poultry establishments that
    retailers can use to control L. monocytogenes.
  • Helpful tools that retail firms can use to identify potential gaps in current best practice procedures.
  • The eight most important recommendations for retail deli operations.

Retailers can use the best practices identified in this guidance to help ensure that RTE meat and poultry products in the deli area are handled under sanitary conditions and are not adulterated, as defined in the Federal Meat Inspection Act (FMIA) and Poultry Products Inspection Act (PPIA).

While these practices are designed to control L. monocytogenes specifically, they also may help control other foodborne pathogens that may be introduced into the retail deli environment and other facilities where consumers take possession of food. No single action or practice will control L. monocytogenes contamination. Therefore, by following the best practices in this guidance and the Food Code, retailers can help ensure that RTE products are not adulterated with L. monocytogenes, and that the potential for listeriosis is decreased.

A Deli Self-Assessment Tool is provided for deli operators in Appendix A of this guidance to help them identify the best practices they are using and to assess whether they need to adopt others.

A Comprehensive Approach: The Eight Most Important Retail Deli Recommendations to Prevent
Conditions That May Cause Adulteration (Source: USDA FSIS

Hepatitis A Outbreak Associated Frozen Strawberries

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By Ryan Maus

A new outbreak of hepatitis A virus has been associated with frozen organic strawberries and sickened five people (with two hospitalizations) from the state of Washington. The strawberries were distributed to numerous retail locations across the country, sometimes comingled with other fruit products. This has led to numerous recalls of products with best by dates as far away as November 2024. The ongoing outbreak serves as a reminder of the hazard viruses can present for certain ingredients and the subsequent products (such as smoothies and juice) in which they are often used.

Outbreaks of hepatitis A are generally reported after epidemiological evidence points to a common food or water source. The virus replicates inside human host cells and is shed in human feces. The virus does not multiply in or on foods but can be transmitted by food and water contaminated with human fecal material. Several fecal-oral scenarios leading to an outbreak include contaminated irrigation or wash water, sick field workers during harvest, or ready-to eat products contaminated by sick food handlers. The current outbreak strain of hepatitis A virus is genetically identical to the hepatitis A strain found in fresh organic strawberries that caused an outbreak in 2022. Organic strawberries in both outbreaks were sourced from farms located in Baja California, Mexico.

Hepatitis A Foodborne Outbreaks (Source FDA and CDC)

YearProductVirusIllness
2023
2022
2019
2017
2016
2016
2013
Frozen Strawberries
Frozen Strawberries
Fresh Blackberries
Frozen Tuna
Frozen Strawberries
Raw Scallops
Pomegranate Seeds 		Hepatitis A
Hepatitis A
Hepatitis A
Hepatitis A
Hepatitis A
Hepatitis A
Hepatitis A		5 (currently)
18
20
Unknown
143
292
162

Berries contaminated with hepatitis A can also pose a hazard when processed into products such as fresh fruit smoothies or juice. A recent warning letter was issued to a juice manufacturer that used contaminated strawberries in the formulation of a high pressure processed (HPP) juice product. The manufacturer did not validate that the HPP treatment would produce the required minimum 5-log reduction to control the target pathogen (hepatitis A virus). Generally, cooking food until it’s at a
temperature of 190˚F in the middle for at least 1½ minutes or boiling food in water for at least 3 minutes inactivates the virus. However, if present, the virus is very hardy and can survive on food, in water, and on environmental surfaces for extended periods of time. Hepatitis A illness usually begins about 2-4 weeks after exposure causing symptoms of fever, low appetite, nausea, vomiting, diarrhea, muscle aches, and jaundice. The virus can clear on its own within a week or two.

However, in some instances, the infection can last up to 6 months and cause inflammation and damage to the liver. Although the virus cannot grow in the
environment, it is considered to be extremely stable under a wide range of environmental conditions, including freezing, heat, desiccation, and chemicals. Concentrations of disinfectants commonly used against pathogenic bacteria might not be effective. A vaccine for the virus has provided a reasonable control measure to prevent the spread of hepatitis A. Preventive measures generally include good food handler hygiene, supplier verification programs, use of potable water, thermal processing, and proper sanitation.

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