Food Safety and Inspection Service United States Department of Agriculture Washington, D.C. 20250-3700

News and Information

May 1999

Listeria Guidelines for Industry

POLICY

The Food Safety and Inspection Service (FSIS) has published a Federal Register notice to ensure that the owners and operators of federally inspected establishments are aware of the Agency’s views about the application of its hazard analysis and critical control point (HACCP) system regulations to contamination with Listeria monocytogenes, and to provide the public with an opportunity to comment on the Agency’s views.

FSIS believes that the findings from testing a range of ready-to-eat products and information from investigations of outbreaks of listeriosis constitute changes that could affect an establishment’s hazard analysis and could alter the HACCP plan for affected products. Therefore, under 9CFR417.4, establishments must reassess their HACCP plans for ready-to-eat meat and poultry products. If reassessment results in a determination that L. monocytogenes contamination is a food safety hazard reasonably likely to occur in the production process, then it is a type of microbiological contamination that must be addressed in a HACCP plan.

The Agency is in the process of revising FSIS Directive 10,240.2, Microbial Sampling of Ready-to-Eat Products Produced By Establishments Operating Under A HACCP System. The revision will address when inspection personnel should not collect product samples for testing by FSIS if establishments are testing. The Agency is considering a policy similar to that contained in FSIS Directive 10,010.1, Microbiological Testing Program For Escherichia coli O157: H7 in Raw Ground Beef. Until FSIS Directive 10,240.2 is revised and issued, inspection personnel will continue to collect product samples regardless of any testing being done by the establishment.

 PURPOSE OF THIS DOCUMENT

The purpose of this document is: (1) to assist establishments that have implemented HACCP and produce RTE product other than thermally processed, commercially sterile, in reassessing their HACCP plans with respect to the hazard that may be presented by L. monocytogenes, and (2) to provide for those establishments that conclude, after such reassessment, that their HACCP plans must address the hazard presented by L. monocytogenes, examples of practices that have been used successfully by other meat and poultry producing establishments to prevent the occurrence of this pathogen in their RTE products.

This document has been assembled using currently available scientific and technical information from within the Agency and other parts of the government, from meat and poultry processing establishments that have shared their successful approaches, and from trade associations that have also shared their collective best thinking on how to handle this difficult problem.

BACKGROUND

The Organism

Listeria is ubiquitous in nature. It is commonly found in the intestines of animals and humans without causing illness. It can survive for long periods of time in soil, leaf litter, sewage, silage dust, vegetation, and water. The organism has been found in many domestic and wild animals, fish, birds, insects, and snails. It has been isolated from a variety of products, including raw milk, cheese made from unpasteurized milk, soft cheese, meat and poultry and their products, cole slaw, and cabbage.

L. monocytogenes bacteria are found frequently in the food-processing environment and can form biofilms on solid surfaces commonly found in the food processing plants, including stainless steel and rubber under experimental conditions. Listeria can also survive adverse conditions on apparently smooth surfaces.

Recent Experiences with Meat and Poultry Products

In recent months there have been several recalls of RTE meat and poultry products because of adulteration with L. monocytogenes. Foodborne illnesses and deaths have been linked to some recalled products. It has generally been concluded that the adulteration occurred through cross-contamination from environmental sources following cooking. Industry for the most part, has identified this as an SSOP failure.

REASSESSMENT OF HACCP PLANS

Below are points to consider when an establishment is developing or reassessing its HACCP plan(s).

• What are the levels of L. monocytogenes on source materials for your products? Do levels fluctuate significantly depending on suppliers? Do levels fluctuate significantly because of your practices regarding the use of rework product in various products?

Raw meat and poultry have been shown to be a source of L. monocytogenes. Knowing the worst possible incoming levels of L. monocytogenes can help you to determine whether your kill step is adequate. Raw materials should be used on a first in, first out basis to minimize time in storage and potential increase in L. monocytogenes levels. Product used as rework because it has been found to be positive for L. monocytogenes in end product testing would add to the microbial load.

Listeria monocytogenes in FSIS Nationwide Sampling Programs

^a Calculated from positive samples only.

• What do your validation results tell you about the efficacy of kill steps used in your processes? What in-plant experience do you have which confirms the efficacy of the kill step you use on products produced from all types of source materials?

Challenge studies, scientific literature, computer modeling programs, and expert advice from processing authorities can be used to validate a HACCP plan. However, the effectiveness of the kill step under actual in-plant conditions would be evaluated through the HACCP plan verification.

• If your products are exposed to an environment not known to be free of L. monocytogenes, what post-kill step controls prevent their contamination by that environment? What do your records reveal about sources of L. monocytogenes in your facility? What do your records tell you about the success of efforts to remove particular sources?

An environmental testing program can be a means of confirming that the establishment’s controls are effective in maintaining a plant environment that will minimize the hazard of pathogens including Listeria monocytogenes. In addition to measuring the effectiveness of a sanitation program, a correctly designed environmental testing program may:

• Provide information about sources of environmental contaminants
• Identify the extent of pathogen contamination of the environment
• Provide information about faulty equipment design or operation
• Identify probable post processing cross-contamination sites

• Do you produce meat and poultry products that will support the growth of L. monocytogenes? What is the basis of your view? What are the implications for storage temperatures and shelf-life?

Currently available information indicates that establishments should view a RTE meat or poultry product as a food that supports the growth of Listeria monocytogenes unless the 1999 Food Code (DHHS, U. S. Public Health Service, FDA) excludes the product from its definition of a "Potentially hazardous food" (excerpts) because (1) the product has an a_w value of 0.85 or less; (2) the product’s pH is 4.6 or below when measured at 24^oC (75^oF); (3) a food, in an unopened hermetically sealed container, that is commercially processed to achieve and maintain commercial sterility under conditions of non-refrigerated storage and distribution; (4) laboratory evidence demonstrates that the rapid and progressive growth of infectious or toxigenic microorganisms or the growth of C. botulinum can not occur, and that may contain a preservative, other barrier to the growth of microorganisms, or a combination of barriers that inhibit the growth of microorganisms; or (5) the product does not support the growth of microorganisms…"

• What does finished product testing reveal about the status of your products with respect to microbial contamination?

FSIS believes that findings of L. monocytogenes in finished product are significant evidence that L. monocytogenes contamination may be a food safety hazard reasonably likely to occur in the production process for that product.

Since 1989, FSIS has conducted finished product testing for L. monocytogenes in several RTE meat and poultry product categories. The results found are as follows:

Listeria monocytogenes in FSIS RTE Sampling Programs, 1989 to present

 CURRENT THINKING ON BEST PRACTICES

A number of trade associations have produced "Best Practice" or GMP documents that cover production practices such as sanitation, raw materials handling, and employee hygiene. These documents are listed in the bibliography; copies may be obtained from these organizations.

 SAMPLING PROGRAMS

The Agency envisions two types of sampling programs that establishments may use: environmental and end product. Environmental sampling includes non-product contact surfaces, such as floors and drains, and product contact surfaces, such as conveyors, belts, slicers, and peelers. End product testing covers RTE product. Examples of testing programs in use in industry are provided in Attachment 1.

Establishments with limited resources should establish end product sampling as their top priority, followed by product contact surface/non-product contact surface testing. A comprehensive flowchart outlining environmental and end product testing is provided in Attachment 2.

ENVIRONMENTAL TESTING: A Commonly Used Tool

Sample Sites and Frequency

Selection of sample sites and sampling frequency for non-product and product contact surfaces depends on establishment features such as plant layout, overhead structures, number of production lines/products, location of processing equipment, and product flow. A sampling protocol should include the sample sites, sample area size, sampling frequency and sample collection techniques. In general, samples sites should be selected randomly. However, some sites may be designated for sampling on a regular basis based on the hazard analysis. Sample size can be determined based on the nature of equipment or surfaces e.g. flat surfaces, inside of equipment, etc. The plan should also detail appropriate, progressive actions the establishment will take as positive samples are found.

Methods

Environmental samples, including swabs and sponges, should be placed in a neutralizing medium immediately after collection, in order to neutralize any residual disinfectants that may be picked up from equipment or other environmental sampling sites. Samples should be stored and shipped to laboratories using standardized procedures. A reputable laboratory should analyze samples. The establishment is responsible for determining the competency of the laboratory used. The laboratory conducting the sample analyses should have properly trained personnel, suitable facilities and equipment, a written quality assurance program that is available to all personnel, and reporting and record keeping capabilities. Presently there is no AOAC-approved method for analyzing environmental samples for Listeria. Laboratories can use published methods after validation. Laboratories can also use FSIS’ L. monocytogenes method published in the Microbiology Laboratory Guidebook, 3^rd edition (Chapter 8, Revision #1, 1/12/99).

An establishment may choose to perform its own indicator organism testing using a screening test. Such tests are available but should be validated as part of the HACCP plan.

Record Keeping

The results of environmental sampling are not available until after products are produced. Therefore, adequate and accurate records are essential because the environmental sampling program is of retrospective value only. For example, identification of the site sampled (drain #1 in peeling room) and the visible condition of the site (clean, smooth surface) is necessary to effectively utilize the sampling results.

Results and Follow-up: Non-product contact surfaces

If positive samples are found from non-product contact surfaces, follow-up actions should be taken, and may include thorough cleaning of suspect areas and equipment with subsequent intensified/expanded testing.

Results and Follow-up: Product contact surfaces

If positive samples are found on product contact surfaces, different follow up actions should be taken, including follow up sampling of product produced on that line, as follows:

1. Once the product contact surface is found to be positive for the number of samples indicated in the HACCP plan for Listeria spp., the next lot of product produced from the line should be sampled and tested for L. monocytogenes.
2. Minimum production time prior to sampling should be determined by the plant and followed. The time may depend on individual line configuration, clean up, and sanitizing procedures. The testing plan should include variations in the time of sampling to detect the increase in Listeria that could occur during the production shift.
3. After product sampling, the line may need to be cleaned and/or operational procedures reviewed, before production of the next lot.
4. The product lot sampled may be held, pending laboratory results.
5. If a sampled lot is found to be positive for L. monocytogenes, and is already in commerce, it will be subject to recall.
6. Product sampling may be intensified, such as testing several consecutive lots. All product produced on positive lines may be held pending laboratory results.
7. After the predetermined number of lots has tested negative for L. monocytogenes, the plant may resume its regular regime of environmental and product sampling.
8. The establishment should document the reason for contamination and steps taken to prevent future incidents.

END PRODUCT TESTING: A Potential Verification Tool

An end product sampling program for RTE meat and poultry products may serve as verification of the HACCP plan. An end product testing program should include several elements, such as sampling frequency, sampling procedures, laboratory methods, follow-up actions, and record keeping. Suggested scientific references that may be helpful are listed in the bibliography.

Sample Frequency and Procedures

The frequency of end product sampling should take into consideration the number and types of different products produced, complexity of processing procedures, the amount of product produced, whether an environmental sampling program is in place, and establishment history. Establishments can base their sampling frequencies on any validated statistical sampling program that achieves their objectives.

Products that have direct exposure to the establishment's processing environment after a kill step is applied may be at greater risk from environmental contaminants than a product cooked and distributed in the same packaging. An establishment may want to increase the frequency of sampling of the former type of products. If no environmental sampling is taking place, more frequent product sampling may be advisable because the early warning of a potential L. monocytogenes problem that environmental sampling may provide will not be available. An establishment that has a prior history of L.monocytogenes findings by either FSIS or its own sampling program may also need to test more frequently.

Sampling should be done as randomly as possible, with all lines and shifts eligible for selection. From the selected lot, multiple sample packages should be collected from the beginning, various middle time points, and towards the end of the production to test a sample representative of the entire lot. Whenever practical, intact packages should be sent to the laboratory for analysis, as they will provide better control of aseptic sampling. Otherwise, an establishment should aseptically collect a portion of each package and place the sample into a sterile bag or other sterile container for shipment to the laboratory.

Methods

Samples should be stored and shipped to laboratories using standardized procedures. A reputable laboratory should analyze samples. The establishment is responsible for determining the competency of the laboratory used. The laboratory conducting the sample analyses should have properly trained personnel, suitable facilities and equipment, a written quality assurance program that is available to all personnel, and reporting and record keeping capabilities. Laboratory methods employed should be AOAC approved or the FSIS L. monocytogenes method published in the Microbiology Laboratory Guidebook, 3^rd edition (Chapter 8, Revision #1, 1/12/99).

Results and Follow-up

If a sampled lot is found to be positive for L. monocytogenes, the establishment should take the appropriate actions.

BIBLIOGRAPHY

 "An Evaluation of the Role of Microbiological Criteria for Foods and Food Ingredients," Subcommittee on Microbiological Criteria, Committee on Food Protection, Food and Nutrition Board, National Research Council, National Academy Press, Washington, DC, 1985.

"Choice of Sampling Plan and Criteria for L. monocytogenes," International Commission on Microbiological Specifications for Foods, International Journal of Food Microbiology 22(1994): 89-96.

"Guidelines for Developing Good Manufacturing Practices (GMPs), Standard Operating Procedures (SOPs), and Environmental Sampling/Testing Recommendations (ESTRs) – Ready to Eat Products," coordinated by National Meats Association, April 1999. (*)
[http://www.nmaonline.org/files/guifinal.pdf ]

"Guidelines to Prevent Post-Processing Contamination from Listeria monocytogenes," National Food Processors Association, submitted to Dairy, Food, and Environmental Sanitarian, April, 1999. (**)

"Interim Guidelines: Microbial Control During Production of Ready-to-Eat Meat and Poultry Products," Joint Industry Task Force on Control of Microbial Pathogens in Ready-to-Eat Meat and Poultry Products, Washington, DC, February 1999. (***)
[http://meatami.org/Guidelines_Microbial_Pathogens_299.pdf   ]

"Microorganisms in Foods, Volume 2, Sampling for Microbiological Analysis: Principles and Specific Applications," 2^nd edition, International Commission on Microbiological Specifications for Foods, University of Toronto Press, Toronto, Canada, 1986.

Sources:

(***)  American Meat Institute
1700 N. Moore Street
Suite 1600
Arlington, VA 22209

(**) National Food Processors Association
1350 I Street, NW
3^rd Floor
Washington, DC 20005

(*) National Meats Association
1970 Broadway
Suite 825
Oakland, CA 94612

Attachment 1: Examples of Environmental Monitoring Programs

Example A

Company A makes ready-to-eat salads, including potato salad, chicken salad, ham salad, etc. for delicatessens in grocery stores. The company manufactures product in two 8-hour shifts, 6 days a week. The third shift is reserved for sanitation. The company targets the salad assembly area in the environmental monitoring component of its L. monocytogenes control program. They have identified three tiers in their sampling program: environmental sampling points, product contact surface points and finished product testing.

They have identified 30 environmental sampling sites, including the walls next to the preparation tables, the exterior of the mixing kettles, the mixer shaft, the drains under the preparation tables, etc. Each week they randomly pick 15 of the 30 sites for testing for Listeria spp.: these 15 sites are tested twice a week ("routine monitoring") before production. Results are tracked as total number of positives over time and also by site. When a positive is detected at any site, it is given extra attention during the next sanitation. If the number of positives exceeds 15% (e.g., if there are 5 positives out of 30) during the week (two test periods, rolling window), or if the same environmental site comes up positive more than 50% of the time in a month, these sites are given extra attention during the next sanitation, and the areas are re-swabbed daily until there are three consecutive days of negatives. Once this has occurred, the plant reverts to routine monitoring. If the problem is not corrected within 5 days, the plant enters the 'trouble shooting" mode, which includes more stringent decontamination procedures, such as disassembly and sanitizing, fogging with sanitizers, changing sanitizers, double sanitizing, and heat treatments.

Company A also conducts routine random product contact surface testing, they have identified 20 key product contact surfaces. Each week 10 of these are randomly selected and tested for Listeria spp. twice a week at the end of production before cleaning. If a positive is detected, the site is given extra attention during the next sanitation and the site is re-swabbed. The site is tested daily for 5 days. If the site is positive twice doing this 5-day period, the line is shut down and, if appropriate, torn apart, taking trouble-shooting swabs during the disassembly. The product contact surface and surrounding areas receive extra sanitation and the line is re-assembled. Product contact surface swabs are then taken every two hours during production and all product is placed on hold. If any swab tests positive, product from the 2-hour time period and from each period on either side is tested for L. monocytogenes. Product that is negative is released. Product that tests positive is destroyed, since re-processing is not an option for this product

The company conducts random product testing of one salad product each month by taking one package every two hours and compositing product from x packages. This results in two tests for each shift of product. Product is tested for L. monocytogenes. Product found to be positive for L. monocytogenes is destroyed and routine product contact monitoring testing for Listeria spp. is conducted daily for a week, with appropriate action taken as described for routine monitoring of product contact surfaces. If product is found to be positive for Listeria spp., including L. monocytogenes, the company undertakes investigations to determine the cause of the problem. The L. monocytogenes control program is also reviewed and revised as appropriate.

Company B

Company B produces fully cooked, breaded chicken products, The company manufactures product on three separate lines in two 8-hour shifts, 6 days a week. The third shift is reserved for sanitation. The company's environmental monitoring component of its L. monocytogenes control program targets the area where product exits the fryer, is chilled and then packaged. There are two parts to this company's program: product contact surface testing and non-product contact surface testing.

The company monitors 20 environmental (non-product contact) surfaces on a weekly basis for Listeria spp, (routine monitoring). Whenever a positive is detected, the company investigates to determine if the positive is an isolated incident by re-sampling the site and by taking additional swabs in the immediate area of the positive. If there are no additional positives, the plant considers the initial positive to be an isolated incident and returns to routine monitoring. If additional positives are detected, the plant institutes corrective actions, which may include a. review of the current L. monocytogenes control program, revising GMPs, changing sanitizes, enhanced sanitation in clean areas, employee retraining, etc. The company then monitors twice a week (enhanced monitoring) until there are 4 consecutive negative periods, at which point the company returns to routine monitoring.

The company also monitors 15 product contact surfaces on each line at the end of each shift of production every other week. For each line, 5 swabs are composited, resulting in 3 tests per line for a shift. If a positive is detected, company investigates by re-swabbing and testing the swabs individually, as well as by taking additional swabs in the area. If the swabs are all negative, they return to routine monitoring. If there is a positive, the plant institutes corrective actions, which may include intensified cleaning, changing sanitizer, etc. The plant then takes swabs to confirm that the actions taken have been effective. If there are no positives, the plant returns to routine monitoring. If there are any positives, the plant escalates its corrective actions, which may include tearing apart pieces of equipment and sanitizing, heating pieces of equipment, etc. They would also evaluate the need to conduct finished product testing based on all the existing evidence. This plant does not conduct any random finished product testing because they have determined that their control program is effective and that such sampling would serve no purpose.

Company C

Company C produces three types of semi-dry, fermented sausages. They have established a control program for L. monocytogenes that targets processing and packaging operations, sanitation practices and personnel hygiene. They do not have a routine environmental testing program; there is limited random testing done in the environment and on some product contact surfaces. The plant has elected to verify the effectiveness of its L. monocytogenes control program through finished product testing. They take one sample from each lot of product and test for Listeria spp. by compositing portions of 5 samples, retaining the remainder. Product is held pending results of the test. If there is a positive, the company tests the retained portions for L. monocytogenes, releasing the negative lots and destroying those that are positive.

For Further Information Contact:
DANIEL L. ENGELJOHN, Ph.D.
Director, Regulations and Directives Development Staff
Food Safety and Inspection Service, USDA
Phone: (202) 720-5627
Fax: (202) 690-0486
E-mail: daniel.engeljohn@usda.gov