What’s on the menu for 2022? Covid-19? Listeria? Salmonella? E. coli?

The year 2021 was a long year, not just for Covid-19, but also for listeria outbreaks in the US. Haskell and DeAngelo review the regulations currently in place to help control listeria outbreaks.

Green sick looking cartoon face.

Kris DeAngelo is an attorney, and teaches several courses with MSU's Institute for Food Laws and Regulations. Scott Haskell teaches the online course “Global Animal Health, Food Safety, and International Trade” each fall semester, and "The Law of the Preventive Controls for Human Food Rule" each spring semester. 

The year 2021 was a long year, not just for Covid-19, but also for listeria outbreaks in the US. Here are some of the recalls and FDA/CDC investigations that took place in the latter part of 2021 alone:

So, what has happened to cause this increase in listeria outbreaks in 2021? Is Covid-19 not enough? And what’s on the menu for 2022?

First, let’s look at the disease agent. Listeria is a Gram-positive, facultatively intracellular rod-shaped bacteria that is environmentally ubiquitous; it can grow aerobically (with oxygen) or anaerobically (without oxygen) and is generally considered an opportunistic pathogen. It grows well at a range of temperatures from -1.5 to 45 degrees C (29.3-113 degrees F), a pH range of 4.0-9.6 and diverse humidity ranges, and even high salt concentrations of 25%.  It even makes a lovely biofilm (think slimely lunchmeat!); and Listeria sp. are omnipresent in nature; commonly found in water, animal intestines and feces, soil, leafy vegetables, raw as well as treated sewage, effluent disposed from meat processing facilities, improperly treated silage, and decomposing produce like soybeans and corn. 

This ubiquitous nature of listeria means that many common foods can be sources of listeria infection including raw vegetables, cooked and raw meats, fermented raw-meat sausages, improperly pasteurized milk, cheeses (especially soft-ripened types including ricotta, Camembert, and traditional Mexican cheeses), ice cream, and cooked, ready-to-eat (RTE) meats, cooked crustaceans, smoked finfish and smoked shellfish, raw seafood, and non-acidic fruit (such as melon, watermelon, and papaya). It has even been found in frozen beef products.

How does it get in these foods? From nature.  Because when listeria isn’t running amuck in humans and animals, it’s a soil decomposing bacterium munching on all types of rotting vegetation in the soil.  It’s growing right where the food is!  Then a little rain or irrigation on growing crops causes water, dirt, bacteria to splash up on the low growing produce, or maybe it ends up on the udders or hides or in the intestines of farm animals and voila! It’s hard to detect, hard to control, and can result in intermittent contamination of food. And consuming listeria containing food can make you sick.

Listeriosis is a serious infection in both humans as well as animals and is most commonly caused by the organism Listeria monocytogenes. Of the seventeen species of listeria, only L. monocytogenes, a few types of L. innocua, and L. ivanovii cause foodborne disease in humans, with L. monocytogenes (Lm) being the most common. Any infection caused by listeria is called listeriosis.

Listeriosis is a relatively rare foodborne disease (in the US ~1600 cases per year). But it is a serious disease with ~94% hospitalization rates (US ~1500) and high fatality rates (approaching 20%-30% depending on location.) The incubation period is long, 17-67 days, making it more difficult to diagnosis. The disease primarily affects older adults, pregnant women, those with weakened immune systems, and newborns, causing gastroenteritis, vomiting, joint pain, headaches.  More seriously in pregnant women Lm causes miscarriage, stillbirth, premature birth, life threatening infections in the newborn, and in non-pregnant persons encephalitis, meningitis, and blood infections.

Listeria is considered a pathogen of significant public health concern. The overall cost estimates for Listeria infections in the US are thought to be from $228 million to $7.6 billion yearly. According to the Centers for Disease Control and Prevention’s (CDC) National Center for Zoonotic, Vector-Borne, and Enteric Diseases, listeriosis was added to the list of nationally notifiable diseases in 2001.

So, what has been done? Not much. Despite an FDA “Action Plan” in 2008, much of that list remains in the discussion stage despite 24 major outbreaks since 2011 alone, including a serious listeria outbreak linked to whole cantaloupes from Jensen Farms in 2011 in which 30 people died.

At least for ready-to-eat (RTE) refrigerated or frozen foods, FDA issued the “Listeria Rule” which requires various steps to be taken to prevent contamination. And while FDA has the authority under FSMA to mandate a recall if a company refuses to issue its own, USDA FSIS does not have mandatory recall authority over meat, poultry, or processed egg products that contain listeria (or other food safety issues).  But USDA can only issue “public health alerts.”  This is not enough.

Similarly, for fresh-cut produce in 2007 FDA issued draft guidance which almost 15 years later is still just a draft with no teeth.

Moreover, various studies have been done in cooperation with Michigan State University, University of Florida, and Florida A&M and the Center for Food Safety and Applied Nutrition (CFSAN). These remain important information guiding plans that have not been approved.

It’s almost 2022.  Come on FDA and USDA, let’s get Listeria off the plate.

During the years 2014 to 2018, 51 foodborne disease outbreaks linked to leafy greens (mainly lettuce) were reported to CDC. Five were multistate outbreaks that led the CDC to issue warnings to the public. Among those, two outbreaks were linked to packaged salads and two were linked to romaine lettuce.

What are the laws and regulations that are in place to help control listeria in food?

The extreme danger associated with the risk of Listeria in RTE products has prompted the USDA to declare the bacteria an adulterant with FSIS Directive 10240.4.

The USDA maintains a zero-tolerance policy for the presence of this deadly pathogen in food. The Code of Federal Regulations includes requirements for the post-lethality control of Listeria in meat and poultry products. This regulation enacted in 2003 is commonly called “The Listeria Rule” (9 CFR § 430.4). The rule outlines the control and prevention that must be undertaken in processing facilities to reduce the risk of contamination of RTE products. According to 21 CFR 117.3, a RTE food means any food that is normally eaten in its raw state or any other food, including a processed food, for which it is reasonably foreseeable that the food will be eaten without further processing that would significantly minimize biological hazards.

9 CFR § 430.4 “Control of Listeria monocytogenes in post-lethality exposed ready-to-eat products” is the primary legislation to help prevent foodborne infections. FDA may regard a RTE food that supports growth of L. monocytogenes to be adulterated within the meaning of section 402(a)(1) of the Federal Food, Drug, and Cosmetic Act (the Act; the FD&C Act) (21 U.S.C. 342(a)(1)) when L. monocytogenes is present in the food based on the detection method indicated in section IV.A.

Let’s look at § 430.4 “Control of Listeria monocytogenes in post-lethality exposed ready-to-eat products” and evaluate how it is to be utilized by the industry:

L. monocytogenes is a hazard that an establishment producing post-lethality exposed RTE products must control through its HACCP plan or prevent in the processing environment through a Sanitation SOP or other prerequisite programRTE product is adulterated if it contains L. monocytogenes, or if it comes into direct contact with a food contact surface that is contaminated with L. monocytogenes. Establishments must not release into commerce product that contains L. monocytogenes or that has been in contact with a food contact surface contaminated with L. monocytogenes without first reworking the product using a process that is destructive of L. monocytogenes.” (Code of Federal Regulations)

In order to maintain the sanitary conditions necessary to meet this requirement, an establishment producing post-lethality exposed RTE product must comply with the requirements included in one of the three following alternatives:

  • Alternative 1.Use of a post-lethality treatment (which may be an antimicrobial agent) that reduces or eliminates microorganisms on the product and an antimicrobial agent or process that suppresses or limits the growth of  monocytogenes. 
  • Alternative 2.Use of either a post-lethality treatment (which may be an antimicrobial agent) that reduces or eliminates microorganisms on the product or an antimicrobial agent or process that suppresses or limits growth of  monocytogenes. 
  • Alternative 3.Use of sanitation measures only.

The establishment must verify that the corrective actions that it takes with respect to sanitation after an initial positive test for L. monocytogenes or an indicator organism on a food contact surface in the post-lethality processing environment are effective by conducting follow-up testing that includes a targeted test of the specific site on the food contact surface area that is the most likely source of contamination by the organism and such additional tests in the surrounding food contact surface area as are necessary to ensure the effectiveness of the corrective actions.

Sanitation measures for controlling L. monocytogenes and procedures for antimicrobial agents or processes that suppress or limit the growth of the pathogen may be incorporated either in the establishment's HACCP plan or in its Sanitation SOP or other prerequisite program. When these control procedures are incorporated into the Sanitation SOP or prerequisite program, and not as a CCP in the HACCP plan, the establishment must have documentation that supports the decision in its hazard analysis that L. monocytogenes is not a hazard that is reasonably likely to occur.

If the measures for addressing L. monocytogenes are addressed in a prerequisite program other than the Sanitation SOP, the establishment must include the program and the results produced by the program in the documentation that the establishment is required to maintain under 9 CFR 417.5.” (Code of Federal Regulations)

Foodborne illness source determination is an important process for estimating food categories that are associated with specific pathogens. As we can see from 2021, listeria is a diverse pathogen associated with a multitude of food sources and environmental outbreaks. Epidemiological studies of disease outbreaks now demonstrate that listeria can cause gastroenteritis in the absence of invasive disease and associated mortality. The determination of multiple data sources is necessary to make attribution estimates.

Determining the many sources of foodborne illness is a key step in identifying opportunities to improve our domestic food safety.

It is important to emphasize that maintaining an improved understanding of the relationship between contaminated foods and disease helps maintain food safety from farm to fork. Continuing listeria research and improving the laws and regulations is an important step in this control and prevention process.





FDA Activities Related to the Listeria monocytogenes Action Plan February 6, 2008


Orsi, RH, Wiedmann, M 2016 Characteristics and distribution of Listeria spp., including Listeria species newly described since 2009  Appl Microbiol Biotechnol. 2016; 100: 5273–5287.


Gambarin, P., et al. 2012 Listeria monocytogenes in Ready-to-Eat Seafood and Potential Hazards for the Consumers. Int J Microbiol. 2012; 2012: 497635. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3384907/pdf/IJMB2012-497635.pdf

FDA. Leafy Green STEC Action Plan. https://www.fda.gov/food/foodborne-pathogens/leafy-greens-stec-action-plan

CDC. Listeria outbreaks 2021. https://www.cdc.gov/listeria/outbreaks/index.html

Legal Information Institute. 9 CFR § 430.4 - Control of Listeria monocytogenes in post-lethality exposed ready-to-eat products. https://www.law.cornell.edu/cfr/text/9/430.4

USDA. Controlling Listeria monocytogenes in Post-lethality Exposed Ready-to-Eat Meat and Poultry Products https://www.fsis.usda.gov/guidelines/2014-0001

FDA. CPG Sec 555.320 Listeria monocytogenes https://www.fda.gov/regulatory-information/search-fda-guidance-documents/cpg-sec-555320-listeria-monocytogenes

CDC. National Listeria Surveillance https://www.cdc.gov/nationalsurveillance/listeria-surveillance.html

Code of Federal Regulations. Title 9. https://www.ecfr.gov/current/title-9/chapter-III/subchapter-E/part-430/section-430.4

Rogalla, D and Bomar, PA 2021. Listeria monocytogenes https://www.ncbi.nlm.nih.gov/books/NBK534838/

FSIS FSIS Directive 10240.4: Verification Activities for the Listeria monocytogenes (Lm) Regulation and the Ready-to-Eat (RTE) Sampling Program.  https://www.fsis.usda.gov/sites/default/files/media_file/2020-08/10240.4.pdf


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