Environmental Sampling and Listeria – New Rules and Responsibilities
What Should a Food Service Manager Do?
Listeria monocytogenes – the words create worry and panic with most food service operators. If not, they certainly should. While Listeria does not cause nearly as many foodborne illnesses as other pathogens, when it does, It is one of the leading causes of death from foodborne illness. It is resilient in nature, salt tolerant (as high as 20% salt) and survives and grows in temperatures where other bacteria can only stay dormant.
As a result of the concern over Listeria, effective January of 2025, the United States Department of Agriculture Food Sanitation and Inspection Service (FSIS) established new tighter sampling and inspection requirements for food processors of ready to eat (RTE) meat and poultry products that have been heat treated and then are subject to further processing.
The USDA FSIS (Food Safety Inspection Service) refers to this as ‘post lethality’, the phase after the kill step (cooking, curing, fermentation or other control measure) in food processing where the product is no longer under the protective control of the kill step.
Why is Post Lethality so Important? The kill step does not kill all bacteria, only enough to make the food safe for consumption. Food is never sterile; some bacteria survive by forming spores to protect themselves, other organisms might contaminate the food during further processing (portioning, packing, labeling). The concern is that foods might be re-contaminated after pathogens have been killed by cooking. At this stage, the food has no active competition to slow any growth of organisms surviving the kill step. While sampling may still be required on Pre-Lethality products, it is critical after the kill step.
USDA vs FDA Licensure Defined – (Here we’re branching out a bit but it’s an important and relevant discussion)
Which food establishments fall under USDA licensing?
The USDA is responsible for meat, poultry, eggs, milk (except fluid milk), catfish, grapefruit and cold pressed raw juice. “Meat” includes beef, pork, lamb and veal; goat; mutton; horse; venison; bison; elk meat from licensed facilities in Colorado and Wyoming. “Poultry” includes chicken, turkey, duck and goose which have no other ingredients or additives. “Eggs” include egg products (dried, frozen, liquid) and the facilities that process them.
USDA also licenses and regulates business which process any of these foods. This includes slaughterhouses, meat, poultry and egg processors, and any processor whose food products have the following characteristics: more than 2% cooked meat, 3% raw meat, 2% cooked poultry meat, or products that contain 10% cooked poultry skins. This last sentence particularly applies to food wholesalers and manufacturers who might produce sandwiches, salads, entrees or other related products.
The FDA regulates all food products sold across State boundaries such as trains and planes, foreign sales, food wholesalers and manufacturers. In addition, the agency regulates shell eggs and their processing plants, juices (not cold raw varieties), meat and poultry products other than those defined above and produce. In most cases the FDA regulates food products while the USDA regulates the unprocessed foods.
Yes, it is a bit confusing and if you have questions, it’s best to ask your inspector for guidance.
Research Note: You might wonder, as I did, why catfish and no other fish are regulated by the USDA. There is history behind this. Under the Federal Meat Inspection Act, catfish are defined as meat. Domestic catfish producers lobbied for this change to allow them to compete against foreign imports.
Back to Sampling: Effective January of 2027, the FSIS has established stricter sampling rules. In addition to existing product testing (usually one pound of post-lethality RTE product), sampling is now required for both Listeria and non-Listeria species, on two food contact surfaces and two non-food contact surfaces. This is in addition to product sampling already in place. Sampling frequency is monthly but can change depending on sample results and sanitation problems in the facility. If you are unsure of the requirements, contact your inspector to review the requirements; they are very detailed.
Unlike food wholesalers, where modified regulations apply to small scale operators, this rule change affects all producers of ready to eat meat and poultry products, regardless of their production volume.
Food wholesalers and manufacturers licensed through State agriculture departments and/or the FDA should already have a sampling program included in their food safety plan. If the operation is only a retail store (e.g., a grocery or deli) and does not manufacture RTE foods under federal rules, or if the facility operator is a small scale entrepreneur, FDA does not require a formal sampling program. Sampling recommendations are included in reference (1) at the bottom of this article.
However, FDA and USDA FSIS recommend such operations adopt Listeria control measures, including environmental monitoring, as part of good food safety. Even the most cursory sampling of surfaces and finished product gives a good measure of the effectiveness of a sanitation program and indicates when and where further efforts are needed.
This blog posting discusses Listeria, how it survives and multiplies and then, how a food service operation can monitor the success of its control strategies. For example, since Listeria outbreaks are so often linked to ready to eat foods in food processing environments, logical controls center around controlling the introduction of contaminated foods into the facility and rapid elimination of any contamination through a comprehensive cleaning and sanitation program. The persistence of listeria can often be traced back to failures associated with prerequisite programs and preventive controls (employee personal hygiene pest control, maintenance of infrastructure).
Listeria Growth Conditions – Growth conditions show that Listeria survives and grows in a wide range of conditions. Temperature – Listeria grows at 34.25 degrees Fahrenheit with the optimum growth range between 86 and 98,6 degrees F. Thus it will grow slowly in ready to eat foods in the refrigerator; this is the reason for the ‘seven day’ date label requirement on ready to eat foods. pH Range – while most pathogens will not grow below a pH of 4.6, Listeria growth has been documented within a range of 4.0 to 9.6. The most significant growth, however, occurs when the pH is above 4.4. Water Activity – Listeria growth occurs when the water activity is greater than 0.92.
There are two forms of the disease: the less severe, non-invasive gastrointestinal listeriosis, and the more severe form, invasive listeriosis, which occurs when the Listeria spreads beyond the intestines. For the less severe, non-invasive listeriosis, mild symptoms such as fever, muscle aches, nausea, vomiting, and diarrhea may occur, and often persists for 1 to 3 days. For the more severe, life-threatening invasive form of the disease, symptoms may include headache, stiff neck, confusion, loss of balance, and convulsions. Invasive listeriosis is a potentially life-threatening event, especially for newborns, adults over the age of 65, and those with weakened immune systems.
Listeria outbreaks in the U.S. have been linked to raw, unpasteurized milk and unpasteurized milk products, certain types of cheeses like pasteurized or unpasteurized queso fresco-type cheese; raw or processed vegetables; raw or processed fruits; raw or undercooked poultry, sausages, hot dogs, deli meats, ice cream; and raw or smoked fish and other seafood. L. monocytogenes has also been found in raw pet food. Listeriosis is most commonly associated with consumption of RTE foods – foods that are consumed without additional cooking prior to consumption, such as deli meats, dairy products, vegetable row crops and fruits. In the past three years, there have been Listeria outbreaks associated with queso fresco, peaches, ice cream, leafy greens, enoki mushrooms, deli meat and cheese.
Onset tine for illness ranges from a few hours to 2-3 days. The more invasive severe form, the one most often associated with patient deaths, can be viable from 3 days to 3 months. If suitable conditions exist, Listeria persists in a food service for years, either on contaminated surfaces or in ready to eat foods. In one case, Listeria isolated from environmental swabs in 2024 was matched to samples from the same facility in 2014!
Food ‘Hurdle’ Effect – Listeria will not grow when foods are formulated to contain a combination of factors. This is called the ‘hurdle’ effect (food operators will hear this term a great deal in the future.). Relying on just one factor such as sanitation or heat treatment will not be enough; there must be two factors such as heat treatment plus pH or water activity control.
While heat treatment will destroy much of the food’s pathogen population, it will not destroy the more resistant strains. No food is sterile, void of bacteria. Nor will heat treatment remove the risk of contamination after cooking. Therefore, the food must have an additional ‘hurdle’ to restrict any further bacterial growth. This might be a low pH or low water activity.
Listeria Environments – Once established in an environment, Listeria forms biofilms on unclean equipment and surfaces, persisting in spite of comprehensive cleaning programs. It survives in such diverse environments (surfaces, drains, air stream) that it can easily move around a facility in the air stream, ponding water or incoming shipments. Further, employees, customers and service personnel can track it around.
Some common harborage points include product coolers, forklifts, forklift stops, hollow equipment legs, dead‐end pipes, drains, floor–wall junctures, junctures between equipment legs and the floor, and floor cracks, among other sites that are difficult to clean and sanitize. Listeria also can be introduced from raw ingredients not requiring a kill step, such as produce, contaminated water (irrigation or processing) or livestock.
It can be introduced by employees, customers, service technicians, anyone entering the production area. Employee hygiene becomes even more critical with Listeria: hand washing and sanitation, wearing gloves, wearing clean coats designated for use only inside of the processing areas, boot washes (or footbaths) at the entrance to the processing areas, and captive footwear policies (e.g., each employee has a set of work boots kept at the facility that may only be used inside the processing areas) – all of these good manufacturing practices become even more critical.
Listeria Foodborne Illness Outbreaks – Between 1998-2023, data from the U.S. Centers for Disease Control (CDC) reported 129 outbreaks resulting in 1517 illnesses, 1191 hospitalizations and 217 deaths. The death rate and hospitalization were calculated at 14% ad 79% respectively. The large majority of these outbreaks (74%) occurred in food processing facilities, probably due to the large volume of food produced. Only 8.5% occurred in retail food establishments (2).
Boars Head listeria outbreak 2024 – deli meats, including liverwurst were involved. 61 people over 19 states were sick, 60 hospitalized with 10 deaths 7 million pounds of product was recalled. The USDA FSIS inspections showed inadequate sanitation practices including the presence of meat and fat residues from the previous days production on packaging equipment; this encourages the development of biofilms, allowing further growth of listeria. Condensation was observed dripping onto exposed product and blown into the air by a fan. Structural problems were observed; cracks, holes and broken flooring could hold moisture. As was described earlier in this article, a failure to observe prerequisite program requirements is a major cause of problems.
Recommendations: So what should a food service operator do to check for Listeria? Since every food service facility will be different, there are only general guidelines established by the FSIS and the FDA. FSIS for instance has general requirements of sampling a pound of post lethality product and a total of four surface samples (two food contact and two nonfood contact); however, the extent of requirements will depend on the facility.
The FSIS and the FDA both establish procedures which are contingent upon the facility’s food products (pH, water activity), the volume of use and production in the facility, type of listeria control program already in place. There are levels of sampling, and sampling frequency, depending on the type of food products (pH, water activity), the volume of use and the type of listeria control program in place (heat treatment, sanitation or a combination of control methods).
The goal of an environmental monitoring program is to:
• Verify the effectiveness of your control programs for L. monocytogenes;
• Find L. monocytogenes and harborage sites if present in your plant; and
• Ensure that corrective actions have eliminated L. monocytogenes and harborage sites when found in your plant.
A well-designed program for monitoring the environment of your plant includes:
• Collecting environmental samples (i.e., collecting samples from FCSs and non-FCSs in your plant);
• Testing the collected environmental samples to identify potential sources of contamination; and
• Taking appropriate corrective actions if test results indicate the presence of Listeria spp. or L. monocytogenes in an environmental sample.
• The best sampling protocol will be for both Listeria spp. as well as Listeria monocytogenes, a subgroup. A positive sample for just L. monocytogenes will leave open the possibility of other Listeria contamination.
A well-designed environmental monitoring program promotes knowledge and awareness of the environmental conditions that could result in product contamination and is a more effective program than product testing alone.
We should emphasize that providing a complete program at this stage is impossible, due to the wide variety of operations. Consult the references at the end of this posting and review the information, in conjunction with consulting your inspector, consultant and other knowledgeable parties.
Cleaning and Sanitizing – Have a written schedule, established based on the volume of production and the frequency the facility is in operation. The food law stipulates cleaning and sanitizing food contact areas at least every four (4) hours under continuous use but those times might change for non-food contact areas, depending on their use;
Evaluate Equipment and Surfaces – Check for structural defects, poor design or disrepair where bacteria could form biofilms or grow.
Evaluate and Maintain Infrastructure – Regularly clean and maintain heating, ventilation and air conditioning systems for accumulated soil, plumbing for leaks floors and walls for cracks and crevices.
Monitor Suppliers and the Movement of Food Products – Listeria contamination can occur in many places prior to the food’s arrival at your facility. Obtain comprehensive letters of guarantee from suppliers and monitor shipments as they arrive. Suppliers should have a listeria control program included in their HACCP plan.
Employee/Personnel Sanitation Program – Listeria can easily be transported throughout the facility by employees and service personnel. Design and institute an employee hygiene program, including hand washing, infection control, clean clothing and footwear.
FDA consumer guidance on Listeria –
https://www.fda.gov/food/buy-store-serve-safe-food/queso-fresco-type-cheeses-consumer-guidance
FDA Bad Bug Book Edition 2
(2) Yuan, Su, Liu, Andres, Zhu, Mei-Jun “Mapping the landscape of listeriosis outbreaks (1998–2023): Trends, challenges, and regulatory responses in the United States” Trends in Food Science & Technology 12/24
(3) Alexandra Belias, Samantha Bolten and Martin Wiedmann “Challenges and Opportunities for Risk- and Systems-based control of Listeria monocytogovenes transmission through food” Comprehensive Reviews in Food Science and Food Safety 111/28/2024
(4) Review of the Boar’s Head Listeria monocytogenes Outbreak January 2025
https://www.fsis.usda.gov/sites/default/files/media_file/documents/Boars-Head-Public-Report-012025.pdf
(5) Saro Loucks “Which Food Products Fall Under USDA Jurisdiction?” FoodReady blog 6/22/2026
(5) Control of Listeria monocytogenes in Ready-To-Eat Foods: Guidance for Industry Draft Guidance https://www.fda.gov/files/food/published/Draft-Guidance-for-Industry–Control-of-Listeria-monocytogenes-in-Ready-To-Eat-Foods-%28PDF%29.pdf
(6) FSIS to Expand Listeria Environmental Sampling Nationwide
The agency will add routine food-contact and non-food-contact surface sampling at ready-to-eat establishments beginning in January 2027.
https://www.qualityassurancemag.com/news/fsis-to-expand-listeria-environmental-sampling-nationwide/