Although trends in Listeria monocytogenes outbreaks are important, it is more concerning that these outbreaks continue to occur despite industry efforts. This article explores the underlying causes of persistent L. monocytogenes outbreaks and emphasizes the need for leadership behaviors outside the food safety function to transform organizational culture to eradicate or manage L. monocytogenes.

Listeriosis Trends and Case Patterns: A 50-Year Overview

Listeriosis, caused by an L. monocytogenes infection, remains a significant foodborne illness, particularly for high-risk populations. Understanding epidemiology and trends in listeriosis is crucial for implementing prevention strategies, mitigating contamination risks, and eliminating outbreaks. This summary examines 50-year global trends in listeriosis and highlights the importance of strengthening the culture of food safety within companies to tackle this persistent issue effectively. 

Early Recognition and Incidence in the 1980s and 1990s
The significance of listeriosis began to emerge in the 1980s, with a marked increase in cases in developed countries. Prior to this, L. monocytogenes was not fully understood as a foodborne pathogen. By the 1980s, however, the U.S. began recognizing it as a significant cause of foodborne illness. Between January 1 and June 14, 1985, 86 cases of L. monocytogenes infection were identified in Los Angeles and Orange Counties, California. Fifty-eight of the cases were among mother-infant pairs, resulting in 13 stillbirths and eight non-neonatal deaths.

The increased recognition of listeriosis in the U.S. and Europe led to heightened awareness of food safety risks in industrial food production systems.¹ The wider application of preventive controls, such as Hazard Analysis and Critical Control Points (HACCP) regulations for meat and poultry production, aimed to improve food safety and reduce the risks associated with listeriosis. These efforts, along with improvements in sanitation practices, were believed to have impact on the number of cases in industrialized countries.²

At this stage, the food safety culture within food companies was focused on meeting regulatory requirements. Many food safety systems were top-down—driven by regulations, rather than internalizing food safety practices within company cultures. However, this period set the stage for the shift toward more preventive measures and proactive food safety systems as awareness of listeriosis grew. 

Rising Awareness and Regulation: 2000s to Early 2010s
The early 2000s saw increasing concerns about listeriosis due to several high-profile outbreaks. While case rates were generally stable or slowly declining, there were still concerns about contamination in certain food products. For example, in the U.S., foodborne listeriosis cases continued to be linked to processed meat. While this food category remains a high-risk product for L. monocytogenes due to the pathogen's ability to grow at refrigeration temperatures,³ many other product categories are now considered high-risk.⁴

In 2000, USDA issued specific directives focused on ready-to-eat (RTE) products⁵ requiring establishments to control L. monocytogenes in post-lethality exposed products. At the same time, countries in Europe began tightening food safety standards and focusing on Listeria monitoring within the food supply chain.⁶

With the growing recognition of the role of food safety culture, leading companies started to incorporate food safety into their organizational cultures. This approach involved employee engagement and cross-departmental collaboration becoming central to food safety practices. The shift toward maturing a culture of food safety, where all employees feel responsible for maintaining the safety of products, aligned well with regulatory changes. 

Major Outbreaks: South Africa and the Global Impact
In 2017–2018, South Africa experienced the world's largest recorded listeriosis outbreak. Over 1,000 people were infected and 216 died, making it the deadliest foodborne illness outbreak in recent history.⁷ The outbreak, which was traced to a contaminated RTE meat product from a single food processing plant, underscored the vulnerability of food production systems to large-scale contamination events. 

The outbreak highlighted gaps in regulatory oversight in certain parts of the world, as well as the need for food safety measures that span the entire supply chain, from raw material sources to final product distribution.⁸ This also underscored the importance of an internalized, forward-thinking food safety culture—where leadership behaviors as well as risk assessment, monitoring, and prevention are at the forefront of operations.⁹

In response, there was a notable shift toward embedding food safety culture more deeply within food companies. In particular, there was a growing recognition that food safety cannot be delegated to a few individuals or departments, but must be integrated throughout every facet of the organization. As a result, food safety learning and leadership's behaviors and ownership of food safety became more central in mitigating risks and ensuring continuous improvement in systems and processes.^10,11

Current Trends and Ongoing Concerns: The 2010s and Beyond
In recent years, listeriosis cases have remained relatively stable in many developed countries, but significant fluctuations are still observed. We are not consistently in control. For example, in 2022, Germany reported 548 cases, and France followed with 451 cases. Across Europe, a total of 2,770 cases were recorded in the 30 EU/European Economic Area (EEA) member countries in 2022, reflecting a slight increase compared to previous years.¹² While these numbers do not suggest a widespread increase in the overall incidence of listeriosis, they indicate that Listeria remains an ongoing concern, particularly in high-risk food products that can support growth before consumption. 

In the U.S., the annual number of reported cases hovers around 1,800, with occasional outbreaks linked to high-risk foods like raw milk, deli meats, cheeses, and more recently, vegetables.¹³ The number of cases in the U.S. has remained relatively consistent, suggesting that food safety protocols in place—including improved monitoring of at-risk foods—are helping to contain, but not reduce, risk. 

The UK has observed a slight rise in listeriosis cases in recent years, with a 12.7 percent increase in 2023 compared to the previous five-year median.¹⁴ While this is concerning, it may also reflect improvements in surveillance and detection methods. The continued occurrence of outbreaks in specific sectors, such as RTE foods, emphasizes the need for ongoing vigilance in food safety management systems. 

Factors Contributing to Sporadic Increases in Cases

The relative stability in case numbers over the past decade does not imply a reduction in risk. Our ability to detect and link more cases has been offset by improvements in Listeria control. Enhanced detection has identified greater sources across more food commodities and products.

Several factors continue to contribute to sporadic increases in listeriosis cases: 

• Outbreaks in specific products. Despite improvements in food safety regulations, periodic outbreaks still occur due to contamination in specific foods. High-risk products like ready-to-eat meats, unpasteurized dairy products, and refrigerated RTE salads continue to be implicated in outbreaks, particularly when hygiene and sanitation measures fail at process control points in food processing.
• Immature organizational cultures. While an increased focus on food safety compliance and culture has been seen, these efforts have not translated into integration of food safety as a business performance indicator. It is continuously left to the food safety and quality department to react and direct food safety—not the C-suite.
• Climate change. The impact of climate change on foodborne pathogens is becoming increasingly evident. Warmer temperatures may influence the growth and persistence of Listeria in food environments, especially in regions where food safety protocols are less stringent.¹⁵ Changing rainfall patterns and extreme weather events may also affect the environmental spread of Listeria in agricultural settings, posing new risks to the food supply chain. 

Systemic and Cultural Failures in Major Listeria Outbreaks

Listeria outbreaks often result from failures in both food safety systems and organizational culture, leading to widespread contamination and illness. Major outbreaks linked to L. monocytogenes include those from Sara Lee (1998–1999), Maple Leaf Foods (2008), Tiger Brands (2017–2018), Jensen Farms (2011), and Boar's Head (2024). Each case highlights systemic issues such as inadequate process controls, weak management, and cultural failures in food safety practices.

Below is a summary of these outbreaks, focusing on systemic and cultural failures, followed by a comparison of key similarities and differences among them (Table 1).

Sara Lee Outbreak (1998–1999)

• Systemic failures: The Sara Lee outbreak in the U.S. was linked to contaminated hot dogs and sliced deli meats. The systemic failures included lack of control during a construction event followed by inadequate sanitation practices, which allowed Listeria to thrive.
• Cultural failures: Sara Lee's food safety culture was undefined at the time of the outbreak. Food safety was viewed as a regulatory requirement rather than an inherent company discipline. As a result, the lack of management commitment to food safety behaviors and protocols was not rigorously enforceable, and employees at all levels lacked training and engagement in maintaining food safety standards.¹⁶
• Post-outbreak response: The outbreak led to cultural changes within the organization, as well as facility improvements, food safety training, and leadership commitment.

Maple Leaf Foods Outbreak (2008)

• Systemic failures: This outbreak occurred in Canada and involved RTE meats. The company failed to maintain proper sanitation practices in its facility. The lack of effective monitoring and internal auditing of the production environment contributed to contamination.
• Cultural failures: Prior to the outbreak, Maple Leaf Foods had not fully embraced food safety as company-wide discipline. The culture of food safety was limited to meeting compliance requirements, and management did not prioritize proactive leadership behaviors.
• Post-outbreak response: After the outbreak, the company shifted to a more proactive food safety approach, including organizational structure and leadership changes, stronger internal controls, and employee engagement in food safety behaviors and practices.¹⁷

Jensen Farms Outbreak (2011)

• Systemic failures: In 2011, Jensen Farms, a U.S.-based cantaloupe processor, experienced an outbreak of listeriosis. The contamination was attributed to lapses in sanitation, inadequate temperature control, and insufficient maintenance of equipment at the production plant. Inadequate cleaning protocols and failure to maintain proper temperature controls allowed the bacteria to grow in the environment.¹⁸
• Cultural failures: As in the prior outbreaks, Jensen Farms did not define and enforce its food safety culture. Food safety practices were often viewed as compliance-driven (regulatory and external audits), not integral to the company's ethos. A failed risk assessment and a lack of proactive communication between employees and management led to failures in addressing potential contamination risks in the plant.
• Post-outbreak response: Eric and Ryan Jensen, the owners and operators of Jensen Farms, each received 5 years of probation and 6 months of home detention, and were each ordered to pay $150,000 in restitution and perform 100 hours of community service. According to the attorneys representing the Jensens, the case "…prompted a new awareness of food safety law and the strict liability imposed on producers and food processors." As a company, Jensen Farms responded by improving its food safety training, implementing better monitoring systems, and making substantial changes to internal procedures.

Tiger Brands Outbreak (2017–2018)

• Systemic failures: The Tiger Brands outbreak was the largest listeriosis outbreak in history, causing over 1,000 infections and 216 deaths. The outbreak was traced to contaminated RTE meat called "polony" that was produced at a single plant operated by Enterprise Foods, a subsidiary of Tiger Brands. Key systemic failures included a lack of regulatory oversight and insufficient internal food safety management at the plant. The plant failed to detect and address environmental contamination, and there was inadequate monitoring of critical control points.¹⁹
• Cultural failures: The cultural failure at Enterprise Foods was significant. The company failed to establish a forward-thinking food safety culture, where every employee, from top management to production staff, took responsibility for food safety. A lack of training, weak communication, and complacency contributed to the persistence of contamination in the plant.¹⁹
• Post-outbreak response: After the outbreak, the South African government implemented stricter food safety regulations and forced industry-wide changes to improve food safety protocols and monitoring.²⁰

Boar's Head Outbreak (2024)

• Systemic failures: In 2024, Boar's Head faced a listeriosis outbreak traced to contamination in its deli meats for slicing at the retail deli. Systemic failures were at the root of the issue, including lapses in sanitation, equipment maintenance, and temperature control at the company's Jarratt, Virginia plant. The company was found to have regulatory compliance and sanitation issues.²¹
• Cultural failures: Food safety culture was a weak point. The company focused on quality, leaving a gap in fully embedding food safety at the core of the company and across all levels of the organization. The outbreak highlighted that food safety was still seen as more of a reactive compliance measure rather than an ongoing, integral commitment to every aspect of the company's operations.¹⁷
• Post-outbreak response: Boar's Head closed the Jarratt plant and created an outside advisory council, but it remains to be seen what post-outbreak actions will sustain the test of time.

Comparison and Contrast of the Outbreaks

Systemic failures 

• Common themes: All five outbreaks involved inadequate integration of foods safety into the organizational culture, poor process control, and failures to recognize sanitary design risks—key factors for the growth of L. monocytogenes in food processing environments. Inconsistent monitoring, ineffective corrective action, and a lack of robust auditing systems were present, allowing contamination to go undetected or persist. 
• Key differences: The Tiger Brands outbreak stands out due to its sheer scale, largely attributed to lack of company and regulatory oversight and the fact that the contamination came from a single plant. In contrast, the Boar's Head outbreak occurred despite numerous regulatory sanitary citations. The Maple Leaf Foods outbreak prompted a company-wide overhaul of food safety practices, and stands out due to the longevity of its food safety changes.

Cultural failures 

• Common themes: In most of these cases, food safety was not sufficiently integrated throughout the company and within the organizational culture. Employees were not fully empowered to take ownership of food safety, and top management did not prioritize food safety as a business performance indicator. Food safety was often treated as a compliance issue rather than a shared responsibility across all levels of the organization. 
• Key differences: The Maple Leaf and Sara Lee outbreaks led to significant cultural changes within the organizations, with both companies investing heavily in facility improvements, food safety behaviors, learning and development, and leadership commitment, as actively demonstrated through leadership decision-making.

So, what is needed to improve on the next 25 years of Listeria control?

Listeria Management: Key Definitions

Growth niche: Location that supports microbiological growth and is protected from the sanitation process.Characterized by high microbial counts after cleaning and sanitation.

Harborage site: Growth niche that contains the pathogen or its indicator organism.

Intervention: Procedure capable of eliminating the pathogen from the affected area (e.g., heat treatment, complete disassembly of the harborage site followed by cleaning and sanitization).

Process control indicator sites: Indicator sites are the measurement system for microbiological process control. They are "risk-based" indicators typically associated with sanitary equipment or facility risks.^22,23

There are three core elements to Listeria control:

1. Eliminate residents
2. Manage pathways of movement
3. Develop and deploy predictive data analysis.

The "seek and destroy" process, developed by co-author Dr. John Butts, effectively addresses the core elements of Listeria control in food processing environments.

The "seek and destroy" process involves the following steps:

1. Risk assessment: Identify equipment and facility design risks. Identify personnel and environmental risks. Measure and manage the risk of scheduled sanitation and maintenance activities.
2. Risk identification: Detect and locate growth niches and harborage sites (i.e., the root causes of contamination) where L. monocytogenes is found or may persist, using risk-driven investigations and aggressive microbiological testing.²³
3. Preventive actions: Develop and implement targeted interventions to eliminate Listeria in harborage sites and to manage growth niches. Physically eliminate risks whenever possible. Optimize sanitation practices to eliminate preoperational failures.²⁴
4. Verification: Evaluate the effectiveness of the implemented interventions and process control activities through ongoing monitoring and testing of the pathways of movement, contact surfaces, and product.²⁵
5. Continuous improvement: Utilize ongoing data analysis to reduce variation in the measured cause and effect parameters. Embrace genomic testing to verify Listeria residence in a facility.²⁶

The "seek and destroy" method has been proven effective in addressing Listeria contamination for over 30 years. Its strong focus on transforming organizational culture from food safety compliance to food safety performance is key.

Managing and measuring food safety performance with the same importance as other key success indicators, such as customer satisfaction and shareholder value, is crucial for leaders in today's complex food industry. Research suggests a correlation between organizational health and safety performance.²⁷ A similar connection likely exists for food safety. However, despite ongoing efforts, both people safety and food safety continue to face challenges, with severe incidents causing significant harm to people and the environment. By integrating effective methods like "seek and destroy" and having a cultural focus on leadership behaviors and food safety performance, organizations can drive meaningful improvements and better protect public health. 

Integrating Seek and Destroy, Leadership Behaviors, and Business Performance

We are proposing a way to integrate the proven "seek and destroy" method with leadership behaviors and success measures (Table 2). Behaviors and measures can be integrated in your leadership's standard work and existing ways of reporting and reviewing business performance.^9,28

Conclusion

While the global trend in listeriosis cases has remained relatively stable, the food industry must continue to remain vigilant. Sporadic outbreaks and localized increases in cases suggest that listeriosis remains a persistent threat, and on a macro level, out of control. Ongoing efforts to improve food safety practices, both at the regulatory level and within food companies, are essential to minimize risks and protect public health. A culture of food safety—where every member of the organization prioritizes and contributes to food safety—will be central in preventing further increases in listeriosis cases and ensuring the safety of the global food supply. 

The Sara Lee,  Maple Leaf Foods,  Jensen Farms, Tiger Brands, and Boar's Head Listeria outbreaks highlight critical systemic and cultural failures that contributed to widespread contamination and consumer harm. While these outbreaks share common systemic issues like inadequate sanitation and lax process controls, they also illustrate how failures in food safety culture can perpetuate risks over time. Companies that failed to embed a mature food safety culture, where food safety is acted on as an integrated and shared responsibility, will be more vulnerable to contamination. In contrast, those that recognized the need for consistent food safety practices and forward-thinking organizational change, like Maple Leaf Foods and Sara Lee, will continue to see reduction in risk and increase in company performance. 

For food company leaders and food safety professionals, these cases serve as powerful reminders of the importance of a mature food safety culture. Compliance-driven actions are insufficient by themselves. A forward-thinking, company-wide commitment to food safety—supported by clear communication, continuous learning and development, and rigorous, data-driven systems—is essential to preventing future outbreaks and keeping consumers from harm. 

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