Food Contamination: Listeria, Salmonella, and Prevention in the Workplace

The bacteria Listeria monocytogenes and Salmonella can cause foodborne illnesses, some of which may be severe. In catering services and the food industry, prevention relies on good hygiene practices, temperature control, the prevention of cross-contamination, and appropriate food safety procedures.

Introduction

Foodborne disease outbreaks are a significant public health concern, particularly in collective catering and food-processing facilities. They may be suspected when several people develop similar symptoms after consuming the same food, according to the criteria used by the relevant health authorities.

Among the bacteria responsible for foodborne illnesses, Listeria monocytogenes and bacteria belonging to the genus Salmonella require particular attention because of their transmission routes and potential health consequences.

Prevention requires control throughout the food chain, from the receipt of raw materials to storage, preparation, and service.

1. Listeria monocytogenes: A Persistent Risk at Refrigeration Temperatures

Listeria monocytogenes is a bacterium capable of surviving and multiplying at refrigeration temperatures when conditions are favourable. Refrigeration slows the growth of many microorganisms but does not guarantee the elimination of this bacterium. Freezing is also not a reliable method for destroying it.

Foods frequently associated with listeriosis include:

• Certain cheeses made from unpasteurised milk.
• Ready-to-eat cooked meats and other deli products.
• Refrigerated smoked fish.
• Certain prepared foods consumed without further cooking.
• Fruits and vegetables contaminated during production, handling, or processing.

Listeriosis is relatively rare but can cause severe complications. The groups at greatest risk include pregnant women, newborns, older adults, and people with weakened immune systems.

In pregnant women, infection can lead to complications affecting the foetus or newborn. Disease severity depends on the form of infection and the population affected. Mortality rates should therefore be reported with their source and context.

Preventive Measures Against Listeria

Workplaces should prioritise the following measures:

• Follow the specified storage temperatures and shelf-life requirements for each product.
• Clean and disinfect surfaces and equipment according to appropriate procedures.
• Prevent cross-contamination between raw materials and ready-to-eat foods.
• Monitor handling and storage conditions.
• Respect use-by dates and storage instructions on product labels.
• Apply monitoring procedures suited to the specific risks of the establishment.

Particular attention should be paid to ready-to-eat foods that may remain refrigerated for extended periods without undergoing any additional heat treatment.

2. Salmonella: Food Contamination and Associated Risks

Bacteria belonging to the genus Salmonella are frequently associated with eggs, egg-based products, poultry, and other contaminated foods. Fruits and vegetables may also be affected, particularly when water, raw materials, or handling conditions are contaminated.

Contamination can occur at different stages of the food chain, including production, transport, storage, preparation, and service.

Non-typhoidal salmonellosis generally causes gastroenteritis characterised by:

• Diarrhoea.
• Abdominal pain.
• Fever.
• Nausea and sometimes vomiting.

Symptoms usually develop between 6 and 72 hours after ingestion, although the incubation period may vary. Most infections are self-limiting, but some can cause severe dehydration or invasive infection, particularly in young children, older adults, and immunocompromised people.

It is important to distinguish non-typhoidal salmonellosis from typhoid and paratyphoid fever, caused by Salmonella Typhi and Salmonella Paratyphi, respectively. These are different diseases and should not be confused with the gastroenteritis usually caused by other salmonellae.

Preventive Measures Against Salmonella

Food businesses should:

• Apply appropriate cooking procedures to prepared foods.
• Prevent contact between raw foods and cooked or ready-to-eat products.
• Clean utensils and work surfaces after handling raw products.
• Maintain the cold chain and comply with storage requirements.
• Use potable water and raw materials from controlled suppliers.
• Train staff in good food hygiene practices.

Food handlers should report episodes of diarrhoea, vomiting, or fever to their supervisor and follow the establishment's procedures before returning to food-handling duties.

3. The WHO’s Five Keys to Safer Food

The World Health Organization recommends five fundamental principles for reducing the risk of foodborne illnesses.

1. Keep Clean

Wash hands at appropriate times, clean work surfaces, and maintain equipment properly. Cleaning and disinfection should follow established procedures.

2. Separate Raw and Cooked Foods

Use appropriate areas, containers, and utensils to prevent microorganisms from raw products transferring to cooked or ready-to-eat foods.

3. Cook Thoroughly

Apply heat treatment appropriate to the food, its size, and the process used. A core temperature of 70°C is a general food safety reference recommended by the WHO for adequately cooking many foods. The applicable parameters must be defined and validated according to the products and relevant regulatory requirements.

4. Keep Food at Safe Temperatures

Refrigerate perishable foods promptly and avoid leaving them at room temperature for extended periods. The WHO's general reference values are refrigeration below 5°C and hot holding above 60°C. However, the applicable limits must take account of the specific food and process requirements.

5. Use Safe Water and Raw Materials

Choose controlled suppliers, inspect products upon receipt, and wash fruits and vegetables thoroughly when necessary.

These five principles should be incorporated into daily staff practices and adapted to the activities of each establishment.

4. The HACCP Method in the Workplace

HACCP stands for Hazard Analysis and Critical Control Points. It is a systematic approach for identifying, assessing, and controlling hazards that may compromise food safety.

Implementation relies on good hygiene practices, hazard analysis, and the definition of control measures appropriate to the processes used.

Key Stages to Control

Receipt of raw materials

• Inspect products and delivery conditions.
• Check temperatures where required.
• Verify traceability information and transport conditions.

Storage

• Maintain the required temperatures for each product category.
• Separate raw products from ready-to-eat foods.
• Respect shelf-life requirements and stock rotation procedures.

Preparation and cooking

• Prevent cross-contamination.
• Monitor defined cooking parameters.
• Verify that planned control measures are correctly implemented.

Cooling and temperature holding

• Cool prepared foods rapidly when required by the process.
• Apply defined and validated time and temperature limits.
• Monitor hot-holding and refrigerated storage conditions.

Traceability and non-conformity management

• Record the checks required by established procedures.
• Define corrective actions when limits are exceeded.
• Establish procedures for suspected or non-compliant products, including isolation and withdrawal where necessary.

Not Every Control Step Is a Critical Control Point

An important distinction must be made between good hygiene practices and Critical Control Points (CCPs). A stage such as receipt, storage, or cooking does not automatically qualify as a CCP.

Classification depends on the hazard analysis, the process, the available control measures, and the HACCP principles applied to the establishment. Critical limits, monitoring methods, corrective actions, and verification procedures must be defined and documented in the food safety system.

5. Food Safety Regulations in Morocco

In Morocco, the National Office for Food Safety (ONSSA) is responsible for food safety control within its legally defined remit.

The regulatory framework includes, in particular:

• Law No. 28-07 on the Safety of Food Products, promulgated by Dahir No. 1-10-08 of 11 February 2010.
• Decree No. 2-10-473 of 6 September 2011, implementing certain provisions of that law.

These texts regulate, among other matters, hygiene and sanitation conditions, health inspection procedures, and requirements applicable to relevant food establishments.

Depending on their activities, food businesses must obtain the required sanitary approval or authorisation and comply with the obligations applicable to them. Specific requirements vary according to the nature of the activity, the products handled, and the regulations in force.

For establishments covered by these requirements, self-monitoring programmes based on HACCP principles and good hygiene practices are important components of food hazard control. The applicable procedures should be verified with ONSSA.

Conclusion

Preventing contamination by Listeria monocytogenes and Salmonella requires a comprehensive food safety approach. Temperature control, staff hygiene, prevention of cross-contamination, and process monitoring are essential to reducing risks.

In food-processing facilities and collective catering establishments, good hygiene practices and an appropriate HACCP system help identify hazards, establish control measures, and protect consumers.

Regulatory compliance must always be assessed according to the establishment's activities and the applicable Moroccan requirements.

Official Sources and References

1. World Health Organization (WHO) — Food Safety: https://www.who.int/en/news-room/fact-sheets/detail/food-safety
2. National Office for Food Safety (ONSSA) — Food Safety Regulations: https://www.onssa.gov.ma/reglementation/reglementation-transversale/securite-sanitaire/
3. Codex Alimentarius — General Principles of Food Hygiene and HACCP: https://www.fao.org/fao-who-codexalimentarius/codex-texts/codes-of-practice/en/