Consequences of Listeria monocytogenes zero tolerance/Not Detected in 25g policy
Contents
Core principles
Testing cannot be a guarantee of food safety
Consequences of having only a Zero Tolerance/ND policy
Reference
Core principles
To manufacture minimally processed foods, i.e. those that cannot be cooked, it is crucial to have and use an approved supply of raw material from reputable suppliers, and a manufacturer that uses HACCP principles, supported by PRPs especially GHP and GMP. All controls therefore need to be validated, verified and monitored to ensure they are robust, and where an adverse result is obtained, immediate remedial action taken. For the control of Lm, environmental monitoring for Listeria species is vitally important to detect inadequate cleaning practices or harbourage points which can potentially harbour Lm in equipment or the environment and grow, potentially contaminating product at unsafe levels.
A complete absence of Listeria monocytogenes (Lm) should always be a commendable goal, however, for certain foods e.g. raw produce and minimally processed foods not processed in pack or handled post-processing in making a final food, it is an unrealistic and unattainable requirement.
Testing cannot be a guarantee of food safety
Not detecting Listeria in a 25g sample does not guarantee absence in a whole batch, and if Listeria is detected in a 25g sample, it does not imply that the whole batch is contaminated. Therefore, confidence in food safety management systems can only be gained by risk assessment, having suitable controls in place supported by PRPs and the regular monitoring of these controls over time to allow remedial action in a timely manner.
Most documented listeriosis outbreaks where a root cause has been identified have been caused by cross contamination post process [1], which has allowed the growth of Lm, either in a long-life product, or in the manufacturing environment where it has not been discovered and actioned. Active and aggressive environmental hygiene assurance is critical to the control of an environmental pathogen such as Lm.
The 100/g limit specified in EC 2073/2005 allows the manufacturer to actively search for Listeria species in the manufacturing environment, in components, in raw materials and verify the control of Lm by testing finished product.
A zero tolerance/Not Detected (ND) approach is an unrealistic expectation and will not remove the fact that Listeria is ubiquitous in the environment and therefore will occasionally be present in minimally processed foods and chilled wet manufacturing environments.
More background to legislative activity
Consequences of having only a zero-tolerance/ND limit include:
- As seen in the USA, testing on finished product will reduce from fear of finding Lm and facing product recalls, with the associated damage to brand reputation and cost to the industry. Practical consequences in the USA include: commercial agreements not to test raw materials/components, lack of information consequently available to food producers to give assurance of safety, or to enable risk-based decisions to be taken, or to have access to safety-related traceability data in the event of an issue. This can result in widescale and/or prolonged withdrawals from the market of contaminated foods, exposing consumers to risk for extended periods of time.
- Testing of food contact surfaces within the manufacturing environment will similarly reduce as this will indicate that the food was in contact with this location and can be deemed to be possibly contaminated. It is standard practice in the USA not to test for Lm given the consequences to businesses.
- Testing will become focused around non-food contact surfaces which may allow sources of contamination to be identified, however cross contaminated food contact surfaces which are then likely to cross contaminate processed food will go undetected, allowing Listeria to grow on the surface over time.
- Subsequent contamination of finished product will also be undetected, putting the health of the consumer at risk.
- A proactive approach to the control of Listeria will be prevented, as potential cross contamination of food contact surfaces or the food itself will not be identified in a timely manner. Contamination, especially of food contact surfaces, must be proactively identified to allow immediate action to be taken. The levels of Lm associated with “unavoidable” contamination of minimally processed products are very low, and the risks are minimal if multiplication does not, or cannot, occur during storage, distribution and preparation. This requires proactive monitoring.
- A zero-tolerance criterion will result in a ‘policing’ of this legislation rather than encouraging FBOs to understand the risk, monitor by taking appropriate samples and putting controls in place to proactively manage Listeria.
- Trending of Listeria results will be limited and the identification of harbourage points or potential biofilms and actioning their removal will be slower, compromising food safety assurance.
The legislation, as currently written in EC 2073/2005, requires an FBO to fully understand their products and proactively routinely monitor for Listeria, keeping any risk to a minimum and allow immediate action to be taken following any detection of Listeria. What is needed is clear guidance to FBOs and enforcers on safe food production for high risk foods with respect to Listeria, and environmental hygiene monitoring and the appropriate use of consequent data to actively and continuously assure food safety.
See Principles of an Environmental Monitoring Program for the Management of Listeria monocytogenes summarising established industry best practice.
Reference
[1] FAO/WHO (2022). 79 of 88 listeriosis outbreaks where a root cause was identified were found to be due to post-process contamination. Annex A2.3 of “Listeria monocytogenes in ready-to-eat (RTE) foods: attribution, characterization and monitoring. FAO/WHO Microbiological Risk Assessment Series, Meeting Report 38. ISSN 1726-5274. (accessed 26 July 2023).
Edited 8 August 2023