Shelf life establishment with respect to Listeria monocytogenes – Epidemiologically Effective Alternatives to Challenge Testing

 

Contents

Core principles
Epidemiological data + conclusions
Schemes and Guidance
CFA Best Practice data + conclusions
Listeriosis outbreaks’ most common root cause + conclusions
Key points regarding challenge testing and assurance of food safety
References

Core Principles


Shelf life establishment using storage trials coupled with day of production (production hygiene) and end of life (monitoring appropriateness of shelf life) sampling of food, with trend analysis including extensive data from environmental sampling has been used by the UK’s chilled RTE food industry supplying its GBP10+bn market for more than two decades. This approach takes into account the effect on Listeria monocytogenes of raw material, process and environmental controls as well as behaviour in the food.

 

Epidemiological Data

EFSA/ECDC epidemiological (Table 1 below) and industry data demonstrate this approach assures safety as it contributes to the UK’s low national listeriosis incidence, which is consistently well below the European average. From 2006 it has been used to also demonstrate compliance with L. monocytogenes criteria in EU Reg 2073/2005, in line with legislative requirements.

Table 1: ECDC/EFSA ONE-Health Listeriosis Rates/100k Population by Country 2016-2021
2017 Case Rate 2018 Cases Rate 2019 Cases Rate 2020 Cases Rate 2021 Cases Rate
Spain 284 – Estonia 272 2.05 Spain 505 – Spain 191 – Spain 224 –
Iceland 6 1.77 Finland 80 1.45 Estonia 21 1.59 Finland 94 1.7 Iceland 5 1.4
Finland 89 1.62 Spain 370 0.89 Iceland 4 1.12 Slovenia 26 1.2 Finland 70 1.3
Denmark 58 1.01 Sweden 89 0.88 Sweden 113 1.1 Iceland 4 1.1 Denmark 62 1.1
Germany 726 0.88 Denmark 49 0.85 Denmark 61 1.05 Malta 5 0.97 Sweden 107 1
Lux 5 0.85 Lux 5 0.83 Malta 5 1.01 Sweden 88 0.85 Slovenia 19 0.9
Sweden 81 0.81 Germany 683 0.82 Slovenia 20 0.96 Denmark 44 0.76 Belgium 65 0.7
Belgium 73 0.8 Belgium 74 0.81 Finland 50 0.91 Norway 37 0.69 France 435 0.64
NL 108 0.63 Latvia 15 0.78 Belgium 66 0.72 Switz 58 0.67 Germany 560 0.67
Slovenia 13 0.63 Lithuania 20 0.71 Germany 570 0.69 Germany 544 0.65 Lux 4 0.63
France 370 0.55 Portugal 64 0.62 NL 103 0.6 Lux 4 0.64 Latvia 10 0.53
Switz 45 0.53 Switz 52 0.61 France 373 0.56 Belgium 54 0.59 NL 86 0.49
Europe* 2,480 0.48 Iceland 2 0.57 Portugal 56 0.54 NL 90 0.52 EU27 2,183 0.49
Portugal 42 0.41 France 338 0.51 Norway 27 0.51 France 334 0.5 EU27+EEA 2,268 0.44
Hungary 36 0.37 Slovenia 10 0.48 Lux 3 0.49 Austria 41 0.46 Austria 38 0.43
Austria 32 0.36 Europe* 2,549 0.47 Europe* 2,621 0.46 Portugal 47 0.46 Italy 241 0.41
Scotland 18 0.33 Norway 24 0.45 Austria 38 0.43 Latvia 8 0.42 Estonia 5 0.38
Lithuania 9 0.32 Ireland 21 0.43 Switz 36 0.42 Europe**  1,876 0.42 Switz 33 0.38
Poland 116 0.31 NL 69 0.4 Hungary 39 0.4 Hungary 32 0.33 Norway 20 0.37
Estonia 4 0.3 Poland 128 0.34 Ireland 17 0.35 Italy 147 0.25 Hungary 35 0.36
Norway 16 0.3 Austria 27 0.31 Italy 202 0.33 Scotland 13 0.24 Poland 120 0.32
Ireland 14 0.29 Slovakia 17 0.31 Slovakia 18 0.33 Cyprus 2 0.23 Scotland 17 0.31
Czech Rep 30 0.28 Czech Rep 31 0.29 Poland 121 0.32 Estonia 3 0.23 Ireland 14 0.28
Italy 164 0.27 Italy 178 0.29 Latvia 6 0.31 UK 148 0.22 UK 186 0.27
UK 160 0.24 Hungary 24 0.25 Czechia 27 0.25 Greece 20 0.19 Lithuania 7 0.25
Slovakia 12 0.22 UK 168 0.25 UK 154 0.23 Poland 62 0.16 Slovakia 13 0.24
Croatia 8 0.19 Scotland 12 0.22 Lithuania 6 0.21 Czechia 16 0.15 Czechia 24 0.22
Greece 20 0.19 Malta 1 0.21 Bulgaria 13 0.19 Slovakia 7 0.13 Greece 21 0.2
Bulgaria 13 0.18 Greece 19 0.18 Croatia 6 0.15 Croatia 5 0.12 Croatia 8 0.2
Latvia 3 0.15 Romania 28 0.14 Scotland 7 0.13 Ireland 6 0.12 Cyprus 1 0.11
Romania 10 0.05 Bulgaria 9 0.13 Cyprus 1 0.11 Bulgaria 4 0.06 Romania 11 0.06
Cyprus 0 0 Cyprus 1 0.12 Greece 10 0.09 Romania 2 0.01 Bulgaria 3 0.04
Malta 0 0 Croatia 4 0.1 Romania 17 0.09 Lithuania 0 0 Malta 0 0
                  Liecht 0 0
Portugal 0 0

 

 

 

 

 

*  Europe = EU28 + EEA + EFTA
** Europe = EU27 + EEA + EFTA

Sources:
UK 2020 data: Food Security Report 2021. Eng+Wales from UKHSA Oct 2022. Scotland from FSS (2021 provisional). UK 2021: UKHSA (provisional).
EU/EEA/EFTSA data: Sentinel system coverage: Belgium: 2016-21 80%, Spain: 2016-21 no info. Human listeriosis data for Switzerland include Liechtenstein to 2020. EU One Health 2021 Zoonoses Report

Conclusions from these data
  1. Epidemiology shows that 100/g limit drives sampling/monitoring, compliance with best practice and when enforced commercially achieves high levels of consumer protection. UK (and IE) listeriosis rates are consistently well below European (EU + EEA + EFTA) mean.
  2. Day of Production (DOP) and End of Life (EOL) sampling, trending and analysis works as a means of demonstrating control and shelf life appropriateness.
  3. Aggressive management of controls including continuous environmental sampling to find Listeria spp, attacking with hygiene and is an effective strategy for factory hygiene control.

Schemes and Guidance

Critically, UK industry recognises the risk to food safety of Listeria monocytogenes in the production environment from potential post-process contamination as full segregation has been implemented for more than 3 decades. Any discovery of Listeria spp. through sampling is followed up by aggressive corrective actions and root cause analysis in ways which are recognised and codified by national and global certification schemes and in Government and industry guidance (Table 2 below).

Table 2. Environmental Management – National and global certification schemes and in Government and industry guidanceView Page
Author Year Title
ANSES, EURL 2012 Guidelines on sampling the food processing area and equipment for the detection of Listeria monocytogenes. Version 3.
BRCGS 2022 Global Standard – Food Safety. Issue 9.
Chilled Food Association (CFA) & British Retail Consortium (BRC) 2006 Guidance on the Practical Implementation of the EC Regulation on Microbiological Criteria for Foodstuffs. Edition 1.2.
CFA & Industry Listeria Group 2023 Principles of an Environmental Monitoring Programme for the Management of Listeria monocytogenes
CFA 2008 Listeria Management Guidance (available to Members and enforcers)
CFA, BRC, Food Standards Agency 2010 Shelf life of ready to eat food in relation to L. monocytogenes – Guidance for food business operators
CODEX Alimentarius Commission 2009 Guidelines on the Application of General Principles of Food Hygiene to the Control of Listeria monocytogenes in Foods CAC/GL 61 – 2007
European Chilled Food Federation 2006 Recommendations for the Production of Prepackaged Chilled Food. 2nd edition.
European Commission 2005 Commission Regulation (EC) No 2073/2005 on Microbiological Criteria for Foodstuffs
European Commission 2013 Working Document re Lm and Shelf life for FBOs (direct download)
Food Safety Authority of Ireland 2005 The Control and Management of Listeria monocytogenes Contamination of Food. ISBN 1-904465-29-3.
Food Standards Scotland 2014, 2022 Safe Smoked Fish Tool
Profel 2020 Hygiene guidelines for the control of Listeria monocytogenes in the production of quick-frozen vegetables.
Ruokavirasto 2020 Elintarvikkeiden mikrobiologiset vaatimukset komission asetuksen (EY) No 2073/2005 soveltaminen sekä yleisiä ohjeita elintarvikkeiden mikrobiologisista tutkimuksista – Ohje elintarvikealan toimijoille. Ohje 4095/04.02.00.01/2020/ 4.
Sainsbury’s Supermarkets. Food Safety Manual, version 2.
USA FSIS 2014 FSIS Compliance Guideline: Controlling Listeria monocytogenes in Post-lethality Exposed Ready-to-Eat Meat and Poultry Products.
US FDA USA FSMA   Key Facts about Preventive Controls for Human Food

 

CFA Best Practice Data

There is a large amount of commercial and Competent Authority experience supporting this approach and an extensive sampling dataset of more than 4 million datapoints underpinning it in our industry alone (Table 3 below for RTE data). This dataset represents >£40m expenditure in sampling and testing, indicating the huge management commitment and resourcing that has been put in the place in UK industry.

Table 3. Chilled Food Association Data: Listeria monocytogenes sampling by UK chilled prepared food producers 2011-2022
RTE food prevalence (1,050,585 samples) ~0.6% Lm at any point during shelf life, of which
~0.01% with Lm present at quantifiable levels, i.e. >20 cfu/g LOQ
RTE production environment prevalence (1,947,956 samples) Food contact surfaces            ~0.3% Lm    (~964k samples)
Non-Food contact surfaces   ~2.5% Lm    (~984k samples)

Source: Chilled Food Association

Conclusions from these data

Criteria 1.2 a/b in 2073/2005 are clear as written, and, when adhered to, provide for a high level of consumer protection. Changing the legislation, particularly as proposed with the *mandatory introduction of challenge testing to set shelf life, critically ignores the prerequisite of assuring and monitoring production area hygiene and continuous routine monitoring of the product.

Standard industry thermal processing of 70°C for 2 minutes equivalent[1] delivers a >6.6 log reduction of L. monocytogenes (D70=0.3). Challenge testing simply demonstrates process efficacy, which is already delivered by HACCP-based systems, with related validation.

 

Listeriosis Outbreaks’ Most Common Root Cause

Post-process contamination is recurrently found to be the root cause of outbreaks[2] (see also FAO/WHO, 2022 and Table 4 below), hence it requires exceptional resourcing. Funds must be spent on environmental controls and hygiene to prevent it in a timely manner, not on unnecessary, costly and narrowly applicable challenge testing.

Table 4: Major Fatal Listeriosis Outbreaks & Root Causes
Country (year) Outcomes and Root Causes
UK (1987-9) >17 dead, 200+ cases. Pâté imported from Belgium. Post-process contamination
France (1992) 92 dead, 272 cases. Jellied pork tongue. Post-process contamination
USA (1998-9) 17 dead, 4 miscarriages/stillbirths, 101 cases. Cooked meat products. Contamination from air filtration unit maintenance. Post-process contamination
Canada (2008) 24 dead, 57 cases. CAD 27m. Cooked sliced meat products. Dirty slicer. Post-process contamination
Denmark (2009) 2 dead, 8 cases. Cooked sliced beef. Post-process contamination
Australia (2009) 4 dead, 8 miscarriages, 35 cases. Cooked sliced meat product. Post-process contamination
Finland (2012) 3 dead, 20 cases. Cooked meat product. Post-process contamination
Denmark (2014) 17 dead, 41 cases. Cooked meat (rullepølse). Post-process contamination
Italy (2016) 4 dead, 1 miscarriage, 24 cases. Cooked RTE meat product. Post-process contamination
South Africa (2017-18) 216 dead, 455 miscarriages, 1060 cases. Cooked RTE meat products. Post-process contamination
Netherlands, Belgium (2017-19) 3 dead, 21 cases. Cooked meat product. Post-process contamination
Spain (2019) 3 dead, 38 miscarriages, 222 cases. Cooked meat product. Post-process contamination
Germany (2019) 7 dead, 1 miscarriage, 112 cases. Cooked meat product. Post-process contamination

See also: Table A2 in Listeria monocytogenes in ready-to-eat (RTE) foods: attribution, characterization and monitoring. FAO/WHO (2022). 79 out of 88 listeriosis outbreaks where a root cause was identified were found to be due to post-process contamination.

Conclusions from these data

Safe food, whether or not challenge-tested to set shelf life, cannot be made in an unhygienic production area. On the other hand, storage trials are proven to be effective in setting shelf life, particularly for short shelf life chilled prepared foods (e.g. 1-10 days), such as those in the UK, Ireland and Finland, and when coupled with DOP, EOL and environmental monitoring data, trending and acting on adverse trends as 2073/2005 requires and as CODEX[3] allows for.

There are additional reasons challenge testing is inappropriate as a mandatory requirement:

  • It cannot replicate factory conditions, nor can it replace the volume of experimental data and professional knowledge which underpin Listeria safety in the UK and Ireland chilled food chain.
  • It does not allow for historical data to be taken into account or data from similar products. The challenge test would only cover an individual product. What happens if very minor changes are made to a product, such as change of a supplier / grower / country of origin. It is impractical to challenge test every time there is a minor change, however these could affect the initial loading.
  • Shelf life would therefore be set by a third party that has no knowledge of the raw materials, manufacturing areas and processes. Food safety is the responsibility of the FBO and Technical experts of the FBO must be involved as they have a detailed knowledge of all aspects of the product and those similar.
  • It does not reflect the actual control of the supply chain resulting in low levels (primarily Not Detected) and low prevalence. The inoculum used in challenge testing is typically a lot higher than is normally detected due to the laboratory needing to aim higher to ensure viable organisms are present. Quorum sensing effects result in exaggerated growth rates from challenge testing compared with realistic levels and prevalence, artificially reducing shelf life.
  • Challenge testing simply demonstrates (e.g. thermal) process efficacy, which is already delivered by HACCP-based systems, with related validation.
  • It does necessarily not reflect production plants’ environmental hygiene where measures such as low ambient temperature and use of biocides stress any Listeria present, reducing viability and vitality.
  • Testing costs per recipe are in the order of EUR10,000-15,000 and results only apply to that particular formulation. It is therefore highly costly in a rapidly changing marketplace and not viable for SMEs in particular. FBOs’ profit margins are generally in the order of 1-2%, so EUR500k-EUR1.5m worth of each food would need to be sold to pay for the cost of its challenge test.
  • It therefore diverts companies’ and Competent Authorities’ money away from implementing meaningful everyday hygiene controls.
  • Hundreds of thousands of different foods around the EU and from countries exporting to the EU would be required to be tested yet there is insufficient laboratory capacity, which would remove foods from the market even if their safety were substantiated through DOP, EOL and environmental data. This would reduce consumer choice and damage SMEs in particular as they are least likely to have technical resource and access to laboratories.
  • Given the high inocula, choice of particularly rapid growing strains and their log-phase status when inoculated, it would result in unnecessary shelf-life reduction leading to an increase in waste, particularly on the Continent where shelf lives are longer than in the UK (Tables 5-10 of the PDF full document), Ireland and Finland, thereby impacting negatively on Climate Change and the EU’s SDG12.3 and food security commitments.
  • DOP/EOL + environmental sampling will always be required by industry to demonstrate manufacturing control, even if challenge testing has been carried out, so it would be an additional cost on manufacture, increasing food prices
  • The EU changing 2073/2005 with respect to criteria 1.2a/b would introduce:
    • requirements that are not in line with CODEX/WTO, so creating a Technical Barrier to Trade, and
    • confusion for enforcement. If for example a food found was to be positive for monocytogenes but had had its shelf life set using challenge testing how would it be treated? Would it need to be recalled?

Durability testing should very rarely be required (i.e. a new factory using new raw materials and a new product process), as shelf life can be determined by the more important sources of information such as product characteristics and historical data etc.

 

Key Points Regarding Challenge Testing and Assurance of Food Safety
  1. Challenge testing should not be mandatory where FBOs have data supporting the safety of their food and performance of their food safety management systems.
  2. Effort should instead be placed particularly on ensuring FBOs have sufficient resources to implement effective preventative actions including cleaning, and monitoring factory hygiene and to undertake aggressive corrective actions if a suspect result is found. This would be the benefit of all industry and society as a whole.
  3. We propose that industry guidance is promoted to FBOs and enforcers setting out effective environmental hygiene management using monitoring and preventative and corrective actions and how to interpret this data and relate it to other results from raw materials, components and product. This would give much-needed detail to support good hygiene practice particularly for SMEs and for enforcement not only by Competent Authorities but also commercially, e.g. by FBOs buying ready to eat ingredients from suppliers and for final product retail customers.

 

For an internationally agreed standard longstanding approach to effective environmental management see: Principles of an Environmental Monitoring Program for the Management of Listeria monocytogenes.


References

[1] ECFF Recommendations for the Production of Prepacked Chilled Food. European Chilled Food Federation (2006)
[2] The Control and Management of Listeria monocytogenes Contamination of Food.  FSAI (2005)
[3] Guidelines on the Application of General Principles of Food Hygiene to the Control of Listeria monocytogenes in Foods CAC/GL 61 – 2007 (2009).


* It is acknowledged that Belgian government guidance exists on challenge testing and Netherlands authorities are requiring challenge testing of various chilled foods

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Edited 8 August 2023