Need to Know

• FDA’s two-day public meeting highlighted the need to reinforce fundamental Listeria monocytogenes controls
• Experts urged regulators and industry to foster a true “seek and destroy” approach in which environmental monitoring is designed to aggressively find Listeria
• Dose-response models suggested that low-level L. monocytogenes exposure may pose relatively low risk
• Retail food safety management systems remain important because L. monocytogenes can grow after food leaves the processing facility
• Although U.S. listeriosis incidence has remained relatively stable, an aging population could increase the disease burden.

Conrad Choiniere, Ph.D., Director of FDA’s Office of Microbiological Food Safety, framed the meeting as an opportunity to reconsider existing approaches rather than assume regulation alone could solve the problem. He called for stronger collaboration among FDA, industry, academia, and public health partners.

“Business as usual is not the best solution,” Dr. Choiniere said, adding that the future of food safety will depend on “shared data, shared science, and shared approaches for managing risk.”

Fundamental Challenges: Listeria Persistence, Sanitation, and Hygienic Design

Across sessions, experts stressed important considerations for ensuring that L. monocytogenes does not become established, spread, and reach food.

Cornell University Professor Martin Wiedmann, Ph.D. described L. monocytogenes persistence as one of the pathogen's most important characteristics, noting that strains can survive in food processing facilities for years. Controlling persistence, he said, could substantially reduce listeriosis risk.

Speakers repeatedly identified hygienic equipment and facility design, cleaning and sanitation, preventive maintenance, hygienic zoning, traffic patterns, moisture control, and prevention of post-lethality contamination as foundational L. monocytogenes controls. Several also argued that sanitation procedures need to be validated to demonstrate that they actually work, rather than merely verified to ensure that prescribed steps are consistently performed.

On moisture control, Joe Stout, R.S., President of Commercial Food Sanitation, urged facilities to “declare war on water,” highlighting relative humidity, condensation, standing water, floors, and other sources of moisture that can support L. monocytogenes survival and growth. Sanitarians cautioned that merely creating the appearance of cleanliness through extensive water use could be counterproductive if facilities are left wet. Moisture management should therefore be considered alongside sanitation, equipment design, and air handling.

Temperature control was also emphasized. Dr. Wiedmann noted that relatively small differences in refrigeration temperatures can meaningfully affect growth and, consequently, risk.

Oregon State University Professor Jovana Kovacevic, Ph.D., discussed specific challenges in produce operations, where L. monocyotgenes naturally occurs in soil, water, and other environmental sources and where equipment and personnel may move between fields and facilities. The discussion highlighted how standing water, soil debris, difficult-to-clean harvest equipment, and equipment designed primarily for product quality rather than hygiene can create L. monocyotgenes control challenges.

A recurring point was that food safety programs need to address real-world operating conditions, especially at small and medium-sized businesses that may lack the resources to replace legacy equipment or employ dedicated microbiological expertise.

True Environmental Monitoring and ‘Seek and Destroy’ Efforts

Speakers from industry and academia stressed that environmental monitoring programs should be designed to find L. monocytogenes, rather than achieve an artificially low positive rate.

For example, Dr. Wiedmann described research in which a small facility collected approximately 300 environmental samples annually without detecting Listeria. When researchers collected only 50 samples themselves, they found three positives.

“We need to set up practices and regulations to encourage plants to find Listeria and control it,” Dr. Wiedmann said. “We cannot overreact to simple positives because facilities then will sample to not find.”

Industry representatives expressed similar concerns that regulatory or corporate responses to positives could unintentionally discourage aggressive environmental monitoring.

Stacy Richardson, Senior Vice President of Enterprise Quality and Food Safety at Schreiber Foods, characterized environmental monitoring as verification that a broader L. monocytogenes control system is functioning, rather than a preventive measure itself. Swabbing, she noted, does not prevent contamination.

“If you have facilities that never have positives, they’re not looking hard enough,” Richardson said. She advocated risk-based and event-triggered sampling, followed by aggressive investigation of the conditions that allowed L. monocytogenes to enter or spread through a facility.

During the public listening session, Casey Gallimore, Senior Director of Regulatory Policy at the Meat Institute, similarly called for a true “seek and destroy” mindset. Such an approach, she said, does not mean finding a positive, cleaning, and repeatedly testing until obtaining a negative result. Rather, companies should continuously search for harborage sites and pathways that could allow contamination to reach product.

Sanjay Gummalla, Ph.D., Senior Vice President of Scientific Affairs at the American Frozen Food Institute, warned against pushing for zero positive findings. “When we push for zero findings, what we really get is no findings,” he said. Low-level contamination that remains undetected, he cautioned, could eventually develop into higher contamination and greater risk.

Dose-Response Science Prompts Debate Over ‘Zero Tolerance’

Day 2 began with an overview of L. monocytogenes dose-response modeling and its potential implications for risk management.

FDA and international experts presented multiple models demonstrating that L. monocytogenes behaves differently from other foodborne pathogens; although the pathogen can cause severe illness, particularly among susceptible people, the probability of invasive listeriosis from low-dose exposure is relatively small.

Consultant Régis Pouillot, D.V.M., Ph.D., M.P.H. described FDA's conservative 2015 dose-response model, which estimated that exposures to 10,000 colony forming units (CFU) or less represented approximately 3.5 percent of U.S. listeriosis cases despite accounting for 99.96 percent of contaminated servings.

Data from a 2015 ice cream-associated outbreak provided an important real-world example. Approximately 15 million contaminated servings were estimated to have been distributed, but the outbreak did not result in a correspondingly massive number of illnesses. The episode provided unusually robust data for evaluating low-dose exposure and supported the conclusion that, at the population level, “low dose equals low risk,” while still demonstrating that widespread low-level contamination can result in illnesses, particularly among highly susceptible people.

Host susceptibility also varied. Modeling presented at the meeting indicated that pregnant women and people with certain cancers can face risks hundreds or thousands of times higher than healthy adults following the same exposure. International modeling also suggested that host susceptibility and strain virulence compound one another.

Rutgers University Distinguished Professor Donald Schaffner, Ph.D., connected the dose-response discussion to sampling and regulatory policy. He emphasized that microbiological “zero tolerance” does not literally demonstrate that zero organisms are present because the ability to detect contamination depends on the number and size of samples collected and the sensitivity of the sampling plan.

Dr. Schaffner argued that it is mathematically possible to design more intensive sampling plans that permit a very low-level positive while providing greater statistical protection than a less-sensitive sampling plan requiring zero positives.

“What if we could incentivize people to look with no penalty for finding very low levels?” Dr. Schaffner asked, noting the “vanishingly small probability” of illness associated with such exposures. He suggested such an approach might encourage manufacturers to conduct more testing and remediate contamination before it increases.

Participants acknowledged that moving from deterministic pass/fail criteria toward probabilistic risk management would involve regulatory, legal, procedural, and communication challenges. Dose-response experts also cautioned that models cannot establish a simple threshold below which every exposure is safe because susceptibility and other variables differ substantially.

Retail Operations Need Practical Food Safety Management Systems

The dose-response modeling discussions reinforced the importance of controlling growth after food leaves production facilities. For example, an international model presented at the meeting estimated that growth between retail and consumption could account for approximately 37 percent of predicted listeriosis cases in the EU, although the effect varied considerably by food, packaging, storage time, and temperature.

This supported the importance of L. monocytogenes prevention in retail food environments, including grocery delis, restaurants, institutional kitchens, and other downstream operations.

FDA representatives emphasized active managerial control, under which the person in charge continuously monitors food safety practices, employees, and equipment rather than waiting for inspectors or problems to identify deficiencies.

Cleaning and sanitation, temperature control, date marking, employee hygiene, prevention of cross-contamination, equipment design, and appropriate product flow were repeatedly identified as core retail interventions. Experts stressed that the retail environment differs fundamentally from manufacturing because operations are open to consumers, labor turnover can be high, and food safety expertise and resources vary widely.

Speakers also stressed that workforce education must evolve. Rather than relying solely on classroom training, participants advocated hands-on demonstrations, short training modules, visual instructions, multilingual materials, coaching, supervisor observations, and competency assessments.

The Aging Population and the Listeriosis Burden

The final scientific session examined how changing demographics and dietary patterns could influence future listeriosis risk.

Because the U.S. population is aging, FDA researchers said national listeriosis incidence would be expected to increase even if foodborne exposure remained unchanged. Instead, incidence has stayed relatively stable over the last two decades. Based on this, experts estimated that L. monocytogenes exposure may have declined by approximately 16 percent during the studied period, suggesting that food safety interventions have offset demographic changes that otherwise would have increased disease incidence.

At the same time, speakers said prevention strategies have not eliminated disparities among high-risk groups. Research presented during the session found that 27 percent of adults aged 60 and older in the studied population fell into dietary-pattern groups ranked highest for listeriosis risk.

Consumer awareness also remains a challenge. Survey data presented during the meeting showed relatively low awareness of Listeria, while many consumers belonging to higher-risk populations did not perceive themselves as particularly vulnerable. Participants also discussed the potential for age-focused warnings to alienate some older adults, highlighting the importance of testing and tailoring risk communications.

Moving Forward: Reinforcing the Basics

Public commenters offered FDA a range of recommendations, including clearer guidance for small and medium-sized processors, greater regulatory recognition of aggressive environmental monitoring, continued focus on foundational controls, and consideration of quantitative or risk-based approaches to L. monocytogenes management.

While advanced technologies like whole genome sequencing (WGS) have improved the ability to connect illnesses with foods and identify persistent strains, speakers cautioned against allowing sophisticated tools to distract from sanitation, hygienic design, moisture and temperature control, maintenance, environmental monitoring, root cause investigations, and workforce competency.