IFR responds to ACMSF Consultation on Listeriosis

Listeriosis is a serious illness in which the rate of mortality can reach 20-30%. Recent years have seen an increase of reported cases of listeriosis in England and Wales and in much of Europe.

Surveys of ready-to-eat, chilled foods sometimes show the presence of Listeria monocytogenes, usually in low numbers. Risks to consumers result from (a) high numbers of L. monocytogenes in a low proportion of samples (b) growth of L. monocytogenes during the shelf-life of foods.

People who are particularly susceptible to infection with L. monocytogenes are those with an impaired immune system (vulnerable groups), these include: persons aged over 60-65, people receiving chemotherapy or radiotherapy treatment for cancer, organ transplant patients, people receiving drug treatment for chronic diseases, pregnant women, and others. These vulnerable groups should avoid certain foods that carry a risk of contamination with L. monocytogenes.

View the Public written consultation document @ http://www.foodstandards.gov.uk/consultations/consulteng/ 2008/acmsflisteriosis

Response from the Institute of Food Research drafted by Dr Barbara Lund.

Comments

Paragraph 2.12 . It is stated that foods associated with outbreaks have been heavily contaminated with the bacterium

Comment. While this is true in many cases, this may not have been true in the outbreak in a tertiary care hospital in Finland in 1998-9 which affected 25 patients, six of whom died. The outbreak strain was detected in 7g packs of butter from the hospital kitchen. The number of L. monocytogenes detected in these packs was between  7 and 79 CFU/g (Lyytikainen et al. 2000; Maijala et al. 2001). In batches from another outlet and from the wholesale store higher levels of L. monocytogenes were detected, but the possibility remains that listeriosis in these vulnerable patients was caused by repeated daily consumption, during many days of hospitalisation, of butter containing relatively low levels of L. monocytogenes.

After the outbreak tests of over 100 samples showed only one batch of 10 pooled samples (from a wholesale store) and one sample from a retailer, cafeteria or institutional kitchen  with >100 CFU L. monocytogenes/g; but the bacterium was isolated from the processing/packaging line at the dairy plant that produced the butter and from drains near the packaging line.

Paragraphs. 4.11, 4.12, 6.12, 6.13.

Comment. Reporting of listeriosis. The efficiency of reporting of cases of listeriosis is fundamental to the subject of this report. In order to address the topic effectively there is a need to ensure that cases are reported.  In England, listeriosis is not a notifiable disease, and would only become notifiable under the heading of “Food Poisoning”.  In reporting four cases of hospital-acquired listeriosis associated with sandwiches, Graham et al. (2002) made the following statement  “In the UK, listeriosis is not a notifiable disease and it is possible therefore that not all cases of listeriosis are either reported or actively followed up. The active follow up of the cases described was facilitated by the apparent nosocomial acquisition of infection and the clustering of cases in time and space. Only a small number of individuals exposed to this agent will develop disease and therefore outbreaks within a hospital may be difficult to detect.”  This is even more true of cases in the community.

Listeriosis is a notifiable disease in France, Germany, Finland, Sweden, Norway, Italy, USA, Canada, Australia and New Zealand.

The report recommends (4.11) that the amount of under-reporting (ascertainment ratio) for human listeriosis should also be estimated, but fails to consider making the disease notifiable.

In order to provide the most effective assessment of the incidence of listeriosis, the disease should be made notifiable in England

Paragraphs 4.31-4.35 and 6.19. It is stated (para 2.17 page 5) that the reported increase in listeriosis since 2000 in the UK and some European countries has occurred almost exclusively in patients aged over 60 years, with bacteraemia.  The hypothesis is discussed that  L. monocytogenes has become more virulent and that  “new” strains are better able to cause bacteraemia.

Comment. There are earlier reports of listeriosis indicating an association between the occurrence of listeria bacteraemia and patients who were immunosuppressed. For example:

• Art and Andre (1991) reported that in adult-juvenile patients in Belgium between 1985 and 1990, listeria bacteraemia, rather than CNS infection, was the main clinical form of illness.
• Data on listeriosis patients in Finland from 1971 to 1989 shows that listeria bacteraemia was more common than meningitis/meningoencaphalitis  in patients with an underlying disease who were treated with immunosuppressive therapy, whereas in patients with underlying disease not treated with immunosuppressive therapy, and in previously healthy patients, meningitis/meningoencephalitis was more common than bacteraemia (Skogberg et al. 1992).
• Bula et al. (1994) described an outbreak of foodborne listeriosis that resulted in a high proportion of CNS infections occurring in relatively young, previously healthy individuals. Patients with bacteraemia were older than those with CNS symptoms and more frequently had underlying conditions.
• In 225 non-pregnant patients in France in 1992, bacteraemia was the most common form of listeriosis in patients with severe immunosuppression and those with other immunosuppressive risk factors, whereas previously healthy patients more commonly had CNS infections (Goulet and Marchetti, 1996).

In the light of these reports and the fact that the increase in listeriosis in the UK since 2000 has mainly been in people aged over 60 with underlying conditions (possibly treated with immunosuppressive agents) it is perhaps not surprising that the predominant symptom has been bacteraemia.

 

Paragraphs 5.27. and 6.34.  It is stated that  “The bacterium has however been found to be present in a number of chilled ready-to-eat foods, usually at low levels, which probably represent a low risk, provided subsequent storage time and temperature conditions are maintained at acceptable levels prior to consumption”.

Comment. It is true that surveys have reported that when L. monocytogenes  was found in chilled ready-to-eat foods it was usually at low levels.  It is important to recognise, however, that in surveys the foods may be sampled well before the end of shelf life, and that a storage temperature of up to 8°C (Food Hygiene Regulations 2005) will allow growth of L. monocytogenes. 

It is also important to consider the incidence of L. monocytogenes in foods in relation to the quantity of the food produced.

For example, Table 7 page 36, in the end of shelf-life study of modified atmosphere and vacuum-packed ready-to-eat meats from retail premises  (Sagoo et al. 2007) the information in the published paper shows that  27 of about 3000 packs contained >10² CFU L. monocytogenes/g at the end of shelf-life and one sample  contained  > 10⁶ CFU L. monocytogenes/g.

These 27 samples came from 8 manufacturers, a large number from one manufacturer.

The number of samples tested was about 3000, but production of such packs of one type of vacuum,/MAP sliced meat (sliced chicken) in England and Wales may be as high as 1.2 x 10⁶ packs per week (data extracted from the National Diet and Nutrition Survey)

If the number of vacuum/MAP packs of all sliced meats produced in England and Wales was 1.2 x 106/week, according to the rates of contamination reported in this survey, 1 x 10⁴ packs per week could contain >100 CFU L. monocytogenes/g at the end of shelf life and 400 packs per week could contain >10⁶ CFU
L. monocytogenes/g at the end of shelf life.
 
In 2007, 230 cases of  listeriosis were reported in England and Wales. In relation to this number, the incidence of L. monocytogenes found in this study of vacuum /MAP sliced meats at the end of shelf-life indicates a significant risk to consumers, particularly vulnerable consumers, and the need for measures to reduce this risk.

Environmental Health Officers  in Norwich report an increase in the number of small producers who are starting to use vacuum/MAP packaging machines to extend the shelf-life of ready-to-eat meat products

Similar consideration should be given to other foods in order to relate the extent of contamination with pathogens to the quantity of the food sold.

Paragraph 4.44. states that “Given the relatively low number of cases of listeriosis that occur every year, even taking into account recent increases, it is possible that poor control at a small number of food businesses manufacturing ‘high risk’ products could be a significant contributing factor, although if this were the case, one might expect to detect local outbreaks rather than sporadic cases.”

Comment. Several factors mean that the consequence of contamination of a product sold in retail shops is likely to be a number of cases of listeriosis that appear to be sporadic.

The following factors are liable to lead to this:

1. a low proportion of the public is liable to develop listeriosis
2. the delay before symptoms develop may vary from 1-90 days
3. the apparently sporadic cases may not be recognized as associated with foodborne transmission, and may not be investigated
4. the disease is not notifiable

 

Paragraph. 4.45 

Comment. It would be useful here to give information about the shelf life of cooked meats, sandwiches, soft cheeses, ready meals, and pâtés

Paragraph 5.4 states that “As currently drafted, criterion 1.2 is open to varying interpretations among Member States and the Commission has produced a Discussion Paper aiming to clarify requirements and promote harmonised implementation of this criterion. The UK’s strict interpretation for products under 1.2b is that there is no criterion for such products when they are placed on the market (i.e. when the manufacturer is unable to demonstrate compliance with the limit of ≤100 cfu/g). In practice, this means if L. monocytogenes is detected when such products are on the market, the Agency would carry out a risk assessment to determine whether any action is required to protect public health. Regulation 2073/2005 is unlikely to provide the legal base for action in these circumstances

Comment.
If Listeria monocytogenes is detected at 10-100/g in a food that allows growth of the bacterium, the following action should be included:

• a check that the records of the food business operator who produced it show that before the food left the control of the producer it showed an absence of L. monocytogenes in 25g
• to determine whether the number of L. monocytogenes is likely to be >100/g at the end of shelf-life. Help with this assessment can be found via the Combase System (www.combase.cc) which is sponsored by the Food Standards Agency (FSA, 2008).

 

Para 5.9  states that chilled, ready-to-eat foods are produced using HACCP principles that aim to identify where the hazard can occur in the manufacturing process and at what steps measures can be put in place to eliminate the hazard or reduce it to an acceptable level (CFA, 2006).

Comment. As stated later  under paragraph 5.15 it should be made clear that microbiological criteria are defined for RTE foods, and the HACCP process includes a verification step in which the foods should be tested to determine whether they meet the criteria.

“The use of microbiological criteria should form an integral part of the implementation of HACCP-based procedures and other hygiene control measures” (EC 2005)

Paragraph 5.20
The advice on the FSA website states that Listeria has been found in certain chilled ready-to-eat foods, such as pre-packed sandwiches, butter, cooked sliced meats, smoked salmon, soft mould-ripened cheeses and pâtés. Vulnerable people should avoid eating pasteurised and unpasteurised cheeses such as Camembert, Brie or Chevre (a type of goats' cheese), or others that have a similar rind, soft blue cheeses, and all types of pâté, including vegetable.

Comment. The vulnerable reader is liable to ask “why is the FSA only advising me to avoid certain cheeses and pâtés?

Paragraph 6.16 states that “Studies should be undertaken to investigate whether trends in the management of conditions which are treated with immunosuppressive or antisecretory agents might have contributed to the overall increase in the risk for listeriosis.”

Comment.  In view of the increase in use of treatment with immunosuppressive agents, this is an important recommendation. Persons undergoing such treatment should be given advice on avoidance of listeriosis.

Paragraph 6.29

Comment. The importance of domestic refrigerator temperatures is mentioned. In order to improve control of temperatures in domestic refrigerators advice should be publicised on the temperatures that should be maintained and on the availability and use of refrigerator thermometers.

Paragraph 6.38.

Comment. Advice should make clear the persons who are in vulnerable groups, and give clear information about foods to avoid.

 

References cited in these comments

Art,D. and André,P. (1991) Clinical and epidemiological aspects of listeriosis in Belgium, 1985-1990. Zentralblatt fur. Bakteriologie 275, 549-556.

Bula, C.J., Bille, J. and Glauser, M.P. (1995) An epidemic of food-borne listeriosis in Western Switzerland: description of 57 cases involving adults. Clinical Infectious Diseases 20, 66-72.

EC (2005) Commission Regulation (EC) No 2073/2005 of 15 November 2005 on microbiological criteria for foodstuffs. Official Journal of the European Union L 338/1 22.12.2005

Goulet, V. and Marchetti,P. (1996) Listeriosis in 225 non-pregnant patients in 1992: clinical aspects and outcome in relation to predisposing conditions. Scandinavian Journal of Infectious Diseases 28, 367-374.

Graham,J.C., Lanser,S., Bignardi,G. et al. (2002) Hospital-acquired listeriosis. Journal of Hospital Infection 51, 136-139.

Lyytikäinen,O., Autlo,T., Maijala,R. et al. (2000) An outbreak of Listeria monocytogenes serotype 3a infections from butter in Finland. Journal of Infectious Diseases 181, 1838-1841.

Maijala,R., Lyytikäinen,O., Johansson,T.  et al. (2001). Exposure to Listeria monocytogenes within an epidemic caused by butter in Finland. International Journal of Food Microbiology 70, 97-109.

Sagoo,S.K., Little,C.L., Allen,G., Williamson,K. and Grant,K.A. (2007) Microbiological safety of retail vacuum-packed and modified atmosphere-packed cooked meats at the end of shelf life. Journal of Food Protection 70, 943-951.

Skogberg,K., Syrjänen,J., Jahkola,M. et al. (1992) Clinical presentation and outcome of listeriosis in patients with and without immunosuppressive therapy. Clinical Infectious Diseases 14, 815-821.