(2001 edition - minor updates July 2012)
These guidelines for packaged ready-to-eat foods found to contain Listeria monocytogenes (L. monocytogenes) were developed in response to the need for a national approach for determining when ready-to-eat packaged products available for sale at retail level have an unacceptable level of contamination and should be recalled.
Similar guidelines exist in the UK, Canada, Denmark and the EU.
These guidelines have been prepared to help state and territory health authorities determine when the presence/level of L. monocytogenes in packaged ready-to-eat foods presents a risk to public health, which may warrant recall action.
A decision to recall should only be made after full consultation with the relevant state or territory health officer. In addition to these guidelines, health officers should consult with the manufacturer on issues such as the extent of the contamination, channels by which the goods have been distributed, and the level to which distribution has taken place, and remaining shelf-life. These factors and any history of illness should be taken into account in determining the appropriate recall level.
This document should be read in conjunction with the 'Food Industry Recall Protocol'
L. monocytogenes is a major foodborne pathogen. Large outbreaks, a high case fatality rate, and the fact that L .monocytogenes can be isolated from a wide range of foods at a time when there is an expanding population of highly susceptible people means that there is a need for continual vigilance and surveillance.
Foods that have been most often associated with human listeriosis are ready-to-eat products that support growth of L. monocytogenes, have a long refrigerated shelf life, and are consumed without further listericidal treatments.
Australia New Zealand Food Standards Code
Standard 1.6.1 includes microbiological standards for L. monocytogenes for a limited number of foods:
- Soft and semi-soft cheese (moisture content >39%, pH >5.0)
- All raw milk cheese, unpasteurised milk and butter
- Packaged cooked, cured/salted meat
- Packaged heat treated pβté and meat paste
- Read-to-eat processed finfish
- Processed bivalve molluscs
The limit generally specified is ‘not detected in 25g’ (sampling plan n=5, c=0, m=0). For ready-to-eat processed finfish, a limit of 100 cfu per 25g is allowed in 1 out of 5 samples (sampling plan n=5, c=1, m=0, M=1).
Microbiological guideline criteria were developed to complement Standard 1.6.1 in the User guide to Standard 1.6.1 – Microbiological Limits for Food with additional guideline criteria. These criteria were intended as advisory criteria for industry and government where failure to meet guideline levels may indicate a failure in process or hygiene procedures and would require corrective action. The User Guide includes ‘not detected’ levels for L. monocytogenes in pasteurised milk, dried milk powder, ice cream and edible ices, powdered infant formula and cereal-based foods for infants.
FSANZ has also developed Guidelines for the microbiological examination of ready-to-eat foods. (RTE Guidelines) to provide assistance in the interpretation of microbiological analyses of foods. They assign four categories of microbiological quality from satisfactory to potentially hazardous and provide recommended actions such as investigation of food handling controls and recall. These guidance documents establish two sets of limits for L. monocytogenes in ready-to-eat foods, based on whether a food is able to support the growth, of Listeria.
Using the approach proposed by the EC, a concentration of L. monocytogenes less than 100cfu/g can be considered to be of low risk to consumers, although the possibility of infection from low numbers of L. monocytogenes, especially among the most susceptible population groups (young, old, pregnant, immunocompromised) cannot be discounted (EC, 1999). However action levels lower than 100 cfu/g will need to be applied for those foods in which growth can occur due to the uncertainty that exists in the estimation of risk for the consumer.
Thus an action level of detected in 25g (10 or >10/g if an enumeration method is used) will be applied to packaged ready-to-eat foods capable of supporting growth of L. monocytogenes, ready-to-eat foods that have been implicated in human listeriosis and foods consumed by high risk groups, to ensure that these foods do not exceed a level of 100 cfu/g at the point of consumption.
Growth and survival characteristics for L. monocytogenes are outlined in the technical information on Listeria under the Agents of Foodborne Illness publication.
These guidelines provide microbiological levels for consideration of proposed recall action but do not provide sampling plans for determining the acceptance/rejection of sample lots. The statistical validity of a microbiological examination increases with the number of field samples analysed. For regulatory purposes, a minimum of 5 sample units from a lot is generally examined. The size of the samples taken should also be adequate to enable appropriate microbiological analyses to be undertaken. A minimum sample size of 100g/ml is commonly required.
A lot can be defined as a quantity of food or food units produced and handled under uniform conditions. This may be restricted to a food item produced from a particular production line or piece of equipment within a certain time period (not exceeding 24 hours).
Field samples taken for laboratory analysis may be limited in number such as, for example, a single sample submitted as a consumer complaint. While the relative microbiological quality of the submitted sample can be made, it may not be representative of the lot from which it is derived. Further samples may be required if an assessment as to the microbiological status of the lot is needed.
The ICMSF publication 'Microorganisms in Foods 2, Sampling for Microbiological Analysis: Principles and Specific Applications' (1986) provides detailed information on using appropriate sampling plans.
For the purposes of these guidelines, ready-to-eat foods are defined as those not requiring any further processing to maintain their safety (will not receive a listericidal treatment) before consumption. Processes such as washing or moderate reheating (<70 degrees C for 2 minutes) are not considered to be listericidal.
For the purposes of these guidelines the term ' packaged food ' means food that has been fully encased in a wrap or container by the manufacturer and is not intended to be unwrapped except by the final consumer of the product.
Food processed correctly and protected from contamination after processing should normally be able to comply with a not detected (less than or equal to 10cfu) in 25g criterion. While a tolerance of 100 organisms per gram is given for packaged ready-to-eat Category 2 foods, the presence of L. monocytogenes in products produced by a process which is capable of achieving a Listeria-free product may indicate that the process is not totally under control. Thus the detection of L. monocytogenes in these foods would be an indication of either inadequate processing or post-process contamination that should be investigated by the manufacturer.
The action levels proposed are for recall purposes only. Manufacturers must still strive for nil tolerance in their packaged ready-to-eat products.
Food categories and Action levels
Category of food
Level of L. monocytogenes
Category 1 - ready-to-eat foods requiring refrigerated storage and able to support the growth of L. monocytogenes*;
- ready-to-eat foods that have been implicated in human listeriosis (e.g. soft & semi soft cheeses, pate, cooked cold chicken, cold-smoked fish**) and/or which may be consumed by at risk groups, especially infants
Detected in 25g#
(Method: AS/NZS 1718.104.22.168- 1998 for the detection of
Category 2 - all other packaged ready-to-eat foods
equal to or greater than 100 cfu per gram
(Method: No AS/NZ enumeration method; see FDA BAM for example for possible methods)
* Factors such as freezing, pH, water activity, lactates and organic acids may inhibit the growth of L. monocytogenes. When it is difficult to predict whether a given food is supportive of growth for L. monocytogenes within the stated shelf-life, the authorities may take a conservative approach and regard growth as possible, unless there is documented evidence provided by the manufacturer that the product does not support growth of L. monocytogenes.
** The Australia New Zealand Food Standards Code as a sampling plan for cold-smoked fish that allows one out of five samples to contain L. monocytogenes up to 100 cfu/g.
*** Equivalent methods may be used AS 5013
# 10 or >10/g if an enumeration method is used.
NOTE: FOODS FOR AT RISK POPULATION GROUPS
The 'at risk' population includes the very young, the very old, pregnant women and the immunocompromised. Foods manufactured specifically for these groups, such as infant foods or foods prepared for hospital feeding, should have a 'not detected’/level of L. monocytogenes.