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Control measures for Listeria monocytogenes in ready-to-eat foods

Important information

This document has been revised to align with Health Canada's Policy on Listeria monocytogenes in ready-to eat foods (2023) that will come into effect on October 1st 2023.

Food businesses should review and adjust their PCP if needed, prior to that date. Until then, industry may use control measures described in the Policy on Listeria monocytogenes in ready-to-eat Foods (2011) or in the updated version (2023).

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1.0 Introduction

Listeria monocytogenes (L. monocytogenes) is widely distributed in nature. It can be found in soil, sewage, vegetation, water, silage, livestock and humans. It is also well adapted to survival in the cold, moist environments commonly found in processing establishments. It can grow at refrigeration temperatures.

Ready-to-Eat (RTE) foods containing L. monocytogenes have been implicated in outbreaks of listeriosis. Certain individuals, including the elderly, pregnant women and immunocompromised are more at risk of serious illness if exposed to L. monocytogenes.

When conducting a hazard analysis for an RTE food, L. monocytogenes should be identified as a hazard that can present a risk of contamination to the food

2.0 Purpose

The Canadian Food Inspection Agency (CFIA) created this document as guidance to help food businesses comply with the Safe Food for Canadians Act and Regulations and Food and Drug Act and Regulations. This guidance is based on Health Canada's Policy on Listeria monocytogenes in ready-to-eat foods (2023) (HC Listeria Policy) and is intended to help food businesses:

This document does not provide information on:

3.0 Roles and responsibilities

Food businesses are responsible for complying with the law. They demonstrate compliance by ensuring that the commodities and processes for which they are responsible meet regulatory requirements. If a written preventive control plan (PCP) is required, the food business develops a PCP with supporting documents, monitors and maintains evidence of its implementation, and verifies that all control measures are effective. If a written PCP is not required, the food business is still responsible to implement preventive controls to ensure their food is not contaminated with L. monocytogenes.

The CFIA verifies the compliance of a food business by conducting activities that include inspection, and surveillance. When non-compliance is identified, the CFIA takes appropriate compliance and enforcement actions.

4.0 Ready-to-eat food category

Refer to section 2.1 of the HC Listeria Policy for a definition of RTE foods and those excluded from the HC Listeria Policy.

RTE foods included in the HC Listeria Policy are classified in 2 major categories based on their potential to support the growth of L. monocytogenes: Category 1 and 2 (2A and 2B). The parameters used to determine the RTE food category are established in the HC Listeria Policy (see Principles for the control of Listeria monocytogenes in ready-to-eat foods in section 6).

If there is uncertainty regarding the categorization of an RTE food, the CFIA should be contacted.

The RTE food categories are used to determine:

5.0 Control measures for L. monocytogenes

Food establishments need to have preventive controls in place that control the hazard of L. monocytogenes in RTE foods. CFIA provides guidance on recommended preventive controls for establishments and for foods that contribute to the control of hazards such as L. monocytogenes:

In addition to these controls, the following measures are specifically applicable to the control of L. monocytogenes in RTE processing environments and products:

5.1 Sanitation controls

L. monocytogenes is known to form colonies of bacteria (biofilms) that attach to a surface. They are commonly found in niches such as closed systems, areas where moisture accumulates and between close fitting materials. These biofilms are surrounded by a protective sheath of proteins and sugars that make them harder to remove.

An effective cleaning and sanitation program prevents L. monocytogenes, that can be present on equipment, food contact surfaces, and in the general premises, from transferring to RTE foods via these venues. The following sanitation controls are effective in preventing the formation of biofilms and removing them should they form:

5.2 Growth limiting parameters

L. monocytogenes can grow at temperatures between –0.4 to 45°C but its growth has been recognized to be prevented in food by:

The product formulation used to prepare a RTE food can be adjusted to limit or prevent the growth of L. monocytogenes.

In order for the growth controlling parameters to be effective, and for the food to remain in the same RTE food category, the physico-chemical parameter target levels have to be met every time the RTE food is manufactured and be maintained for the duration of the stated shelf-life. You can ensure this by:

Note: A change in the product formulation could impact the effectiveness of growth  controlling parameters. The new product formulation may  need to be validated and the category of the RTE food may have to be reviewed and confirmed by the CFIA.

5.3 Food additives and processing aids

Some food additives can control the growth of micro-organisms. The food additives authorized for use as an antimicrobial agent are those found in Health Canada's Lists of permitted food additives.

The use of an antimicrobial food additive can affect the categorization of a RTE food under the HC Listeria Policy. For instance, a Category 1 RTE food can be re-categorized as a Category 2B when the validation of the antimicrobial agent used demonstrates that the growth of L. monocytogenes does not increase by more than 0.5-log CFU/g throughout the stated the shelf-life of the product.

If the antimicrobial food additive limits the growth of L. monocytogenes to less than 2-log CFU/g throughout the stated shelf life of the RTE food, the recommended sampling frequency for environmental sampling and finished product testing can be reduced based on a lower relative risk level (RRL)–see Tables 1-3.

Antimicrobial processing aids can also be used to decrease the levels of micro-organisms, such as L. monocytogenes. It should be noted that, the categorization of the RTE food under the HC Listeria Policy will not be affected by the use of food processing aids, because processing aids do not remain in the RTE food and hence do not affect growth of L. monocytogenes during the stated shelf life. Health Canada maintains a List of Antimicrobial Food Processing Aid for Red Meat and Poultry Meat for Which Health Canada has Expressed No Objection.

5.4 Shelf life validation

The shelf life of an RTE food is affected by factors such as the:

The shelf life should take into consideration these factors and be limited to the length of time the RTE food can be stored without affecting its quality and safety. The shelf life is validated to ensure that the RTE food will remain safe for consumption. See Shelf-life studies for guidance.

5.5 Post lethality treatment

A post-lethality treatment such as surface heat pasteurization (by steam, hot water, radiant heat or infrared technology) and high pressure processing can be applied to packaged RTE foods to reduce or eliminate L. monocytogenes that may have been introduced onto the RTE food after the lethality treatment. These treatments can be used alone or in combination with an approved antimicrobial agent.

If the post-packaging treatment is validated to achieve a 3-log reduction or more of L. monocytogenes, the recommended sampling frequency for environmental sampling and finished product testing can be reduced based on a lower relative risk level (RRL), see Tables 1 to 3.

6.0 Monitoring effectiveness of Controls

6.1 Environmental sampling program

Sampling and testing the areas where the food is prepared, as well as the equipment used to prepare the food, will determine the presence of Listeria. This is important to confirm whether the controls you have applied are effective. Testing non-FCS is a valuable tool to detect potential sources of Listeria in the establishment before it reaches FCS.

Section 7.2 and figures 2, 3 and 4 of the HC Listeria Policy provides guidance on environmental sampling of both food contact surfaces (FCS) and non-food contact surfaces (NFCS). The MFLP-41- Environmental Sampling for the Detection of Microorganisms method, available in Health Canada's Compendium of analytical methods, provide guidance on sampling materials, procedures, sampling sites and how samples are to be handled and transported.

Your environmental sampling program should outline:

6.1.1 The target organism to be analyzed

Monitoring the presence of all Listeria spp. in the environment provides a better indication of the effectiveness of the control measures than testing only for L. monocytogenes.

6.1.2 Sampling sites

6.1.3 Sampling materials, method and procedures used to conduct and collect swabs (such as sterile sponges or cotton swabs) of environmental samples

6.1.4 Sampling Frequency

Table 1 presents recommended FCS testing frequencies when preparing the highest risk Category 1 RTE food.

Table 1: FCS testing frequency per production line according to the relative risk level for the highest risk Category 1 RTE foods: Deli meat products Table Note a, Hot-dogs, smoked seafood and cooked ready to eat crustaceans Table Note b
Production volume Table Note c No antimicrobial agent or post-lethality treatment Antimicrobial agent Table Note d Post-lethality treatment Table Note e Antimicrobial agent and post-lethality treatment
Very small Once per month Once every 2 months Once every 2 months Once every 3 months
Small Twice per month Once per month Once per month Once every 2 months
Medium 3 times per month 3 times every 2 months 3 times every 2 months Once per month
Large 4 times per month Twice per month Twice per month Once per month

Table 2 presents recommended FCS testing frequencies for RTE foods not covered by Table 1

Table 2: FCS testing frequency per production line according to the relative risk level (RRL) for RTE foods not covered by Table 1
RTE risk category No antimicrobial agent or post-lethality treatment Antimicrobial agent Table Note f Post-lethality treatment Table Note g Antimicrobial agent Table Note f and Post-lethality treatment Table Note g
Category 1 Once per month Once every 2 months Once every 2 months Once every 3 months
Category 2A Once every 3 months Once every 6 months Once every 6 months Once per year
Category 2B Once every 6 months N/A Once per year N/A

It is strongly recommended that you hold the food being produced during the environmental sampling because it may need to be tested if the test results are positive. Having the food under your control makes follow-up activities easier.

6.2 Finished Product Sampling Program

Testing the finished RTE food for the presence of L. monocytogenes is used to determine whether the controls applied to prevent the introduction of L. monocytogenes into RTE foods are effective. However, positive results for L. monocytogenes may not provide information on the cause or source of Listeria, which control measure is ineffective or whether additional measures need to be applied. Further, the presence and level of L. monocytogenes may differ between units within a lot of RTE food, and therefore not be detected through testing, even if present. Therefore it is important that final product testing for L. monocytogenes is coupled with an environmental sampling program as described in section 6.1.

Section 7.3 and Table 1: Sampling methodologies and microbiological criteria for Listeria monocytogenes in ready-to-eat foods in the HC Listeria Policy provide guidance on the sampling and testing for each RTE food category.

Your RTE food sampling and testing program should outline the following:

6.2.1 Sampling materials, methods and procedures

6.2.2 How the samples are identified in order to link the test results to the RTE food produced and tested

Samples should be identified using :

6.2.3 The sampling frequency for each RTE food

Testing frequency should be based on:

Table 3 presents recommended finished product testing frequencies.

Table 3: Product sampling frequency according to the relative risk level (RRL)
RTE risk category No antimicrobial agent or post-lethality treatment  Antimicrobial agent Table Note h Post-lethality treatment Table Note i Antimicrobial agent Table Note h and post-lethality treatment Table Note i
Category 1 Once per month Once every 6 weeks Once every 6 weeks Once every 2 months
Category 2A Once every 2 months Once every 3 months Once every 3 months Once every 6 months
Category 2B Once every 6 months N/A Once per year N/A

For an establishment producing RTE foods under different RRLs, the establishment's sampling frequency should be established based on the RTE food with the highest RRL. For a given sampling frequency, higher risk products should be sampled at a proportionally higher rate.

6.3 Considerations for increasing environmental and product sampling frequency

Tables 1, 2 and 3 provide minimum expectations with regard to sampling frequencies accounting for RTE foods with varying risk levels based on the use of post-processing and/or antimicrobial treatments. However, increasing the sampling frequency by 50% is recommended for the following RTE products:

Note also that, while sampling frequencies in Tables 1, 2 and 3 do not apply to RTE products excluded from the HC Listeria Policy, sampling of these products at Cat 2B frequency, as a minimum, should be considered, particularly if they have been associated with outbreaks. See requirements and best practices for foods excluded from the policy in section 2.1.1.1 of the HC Listeria Policy.

6.4 Laboratory Procedures

6.4.1 The following laboratory procedures are applicable to environmental FCS testing and finished product testing

7.0 Follow-up procedures

Follow-up procedures are set out in Figures 2, 3 and 4 of the HC Listeria Policy. These procedures include taking corrective actions as soon as possible when environmental samples are positive for Listeria spp. and food samples are positive for L. monocytogenes. Note: The finding of L. monocytogenes on a FCS should trigger follow-up actions as described in Figure 2, Step B or Figure 3, Step C of the HC Listeria Policy, as applicable. 

You can determine in advance, and describe in your PCP, the corrective actions you should take when there are positive results. They should include:

7.1 Food Contact Surface samples positive for Listeria

7.1.1 Examples of corrective actions

Verify the effectiveness of corrective actions in accordance with Figures 2 and 3 of the HC Listeria Policy.

7.1.2 Persistent contamination

If two or more FCS samples from the same production line (for example: using the same equipment) are found positive for Listeria within a short timeframe, this is considered persistent contamination and an indication that the sanitation procedures or Listeria control measures are inadequate.

As indicated in the HC Listeria Policy, section 7.2.1.1, what constitutes a "short" timeframe is operation-specific and will vary based on factors such as production volume, production seasonality and testing frequency. It should be considered that persistent contamination exists when an increase in the rate of FCS contamination is observed in the establishment's trend analysis.

In these situations it is recommended to:

7.1.3 Review of sampling and testing program

In the aftermath of a persistent contamination event, the sampling programs should be reviewed to determine whether there is a need to update, for example, whether the sampling frequency may need to be increased and whether the sampling sites are adequate.

7.2 Non-Food Contact Surface samples positive for Listeria

Follow-up procedures are set out in the HC Listeria Policy, Figure 4.

The presence of Listeria on NFCS is an indication that improvements are needed to the maintenance and operation of the establishment.

Follow-up procedures are implemented based on the potential for product contamination taking into consideration surfaces that routinely come in contact with an object that is in direct contact with an exposed RTE food or FCS without a sanitizing step, such as:

7.3 RTE food samples positive for L. monocytogenes

7.3.1 Implement corrective actions (see section 7.1.1) in addition to the following activities

7.3.2 Verification of effectiveness of corrective actions

The same food that tested positive for L. monocytogenes under the initial sampling plan should be sampled under hold-and-test procedures. If not available, another RTE food (preferably similar) prepared on the affected line can be selected.

Corrective actions are considered effective when FCS samples test negative for L. spp and RTE food samples test negative for L. monocytogenes for a period of 5 consecutive days.

7.3.3 Re-conditioning of RTE product found positive for L. monocytogenes

A heating process validated to achieve full lethality (5-log reduction in L. monocytogenes) is an acceptable re-conditioning method. Non-thermal processes, such as high pressure processing (HPP), must be evaluated on a case-by-case basis to determine whether they achieve a 5 log reduction in L. monocytogenes.

It is recommended establishments consult CFIA if they plan to re-condition product found positive for L. monocytogenes.

7.3.4 Presence of L. monocytogenes at low levels in category 2 products produced for consumption by the general public

While the presence of L. monocytogenes at low levels (≤ 100 cfu/g) in a category 2A or 2B product, does not require taking action on the product under most circumstances, it can be an indication of a possible loss of control and should prompt the operator to verify and/or re-evaluate their process and control measures.

It is recommended establishments consult with CFIA when such situations occur.

8.0 Trend analysis

Performing a trend analysis of the test results is an essential component of any sampling program designed to monitor a microbiological risk. Trend analysis allows you to identify a potential loss of control or inadequate controls that can be corrected before they result in non-compliance. For example, corrective measures could be taken when the trend analysis shows that:

The trend analysis procedures should:

References and further reading

The following references contain information that helps to explain food safety controls, demonstrates how to develop them, and provides examples. The CFIA is not responsible for the content of documents that are created by other government agencies or international sources.

CFIA references

Further reading

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