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Listeria monocytogenes Risk Assessment: Summary of Public Comments and FDA/FSIS Revisions, Contributors, and Acknowledgments

FDA/Center for Food Safety and Applied Nutrition
USDA/Food Safety and Inspection Service
September 2003


Summary of Public Comments and FDA/FSIS Revisions to Risk Assessment

A notice of availability of a draft risk assessment on the relationship between foodborne Listeria monocytogenes and human health, and a proposed risk management action plan was published in the Federal Register of January 19, 2001 (66 FR 5515) by the Food and Drug Administration (FDA), in cooperation with the Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA), and the Centers for Disease Control and Prevention (CDC). As part of a peer evaluation of the draft risk assessment, FDA/FSIS requested comments on the technical aspects of the draft risk assessment in the following areas: (1) the assumptions made; (2) the modeling techniques; (3) the data used; and (4) the transparency of the document. Comments were solicited for a 60-day period, ending March 20, 2001. Extensions were granted to comment on the risk assessment, extending the comment period to July 18, 2001.

We received 20 submissions of public comments. Submissions to the docket were received from: consumer groups; industry; trade associations representing the food industry, restaurants, food processors, manufacturers, distributors, marketers; consumer groups; manufacturer of food processing equipment; expert risk assessors and modelers; food retailer; educational and scientific society; and marketer, processor and distributor of agricultural and food products. The specific comments and the corresponding FDA/FSIS action/response for each topic area are described in Appendix 2.

We wish to both acknowledge and express our appreciation to those who provided comments to us. We considered the specific public comments in preparing this revised risk assessment. On the basis of the comments received, we determined that certain modifications should be included in the revised risk assessment. These modifications include the following.

  1. Revision of the Food Categories
    • The cheese categories have been reorganized into six categories based on moisture content.
    • The Miscellaneous Dairy Products have been split into two categories: Cultured Milk Products (includes the low pH dairy foods manufactured with lactic acid fermentation) and High Fat and Other Dairy Products (includes the remainder of the dairy products that generally support growth).
    • The frankfurter category was separated into reheated and not reheated frankfurter categories.
    • Vegetable and fruit salads with salad dressing (including cole slaw and potato salad) were moved to the Deli-type Salad food category.
    • Canned fruits and nuts were removed.
    • Pickled, dried, and processed vegetables were removed.
    • The number of food categories was increased from 20 to 23.
  2. Modifications to the Contamination Data
    • Newly available published and unpublished contamination data (approximately 40 studies) were included.
    • Contamination data were weighted according to geographical location, year collected, and study size and an adjustment factor was used for food categories that had no new data.
    • Food category-specific generalizations were made for the shape of the Listeria monocytogenes concentration distributions based on enumeration studies.
  3. Modifications to the Growth Data
    • Newly available data on growth of Listeria monocytogenes in various foods and post-retail storage times (frankfurters and deli meats) were included.
    • For the Deli-type Salad food category, salads were segregated into growth and non-growth salads (and included consideration of the use of preservatives in salads made for bulk distribution to retail stores).
    • For non-growth foods, the rates of inactivation were estimated from the research literature.
    • The percentage of Frankfurters frozen before consumption were excluded from the growth model.
  4. Incorporated Key New Data:
    • American Meat Institute (AMI) consumer survey on how long (on average) deli meats and frankfurters were stored prior to consumption.
    • National Food Processors Association (NFPA)/ Joint Institute for Food Safety and Applied Nutrition (JIFSAN) retail study, detailing the frequency and prevalence of Listeria monocytogenes in deli meats, deli salads, bagged fresh vegetables, seafood salads, smoked seafood, soft cheeses, and Hispanic-style cheeses.
    • FDA/CFSAN study on the growth of Listeria monocytogenes in deli salads.
    • International Dairy Foods Association (IDFA) data on cheese and ice cream.
    • Refrigerated Foods Association study in growth of Listeria monocytogenes in deli salads.
  5. Dose-Response and Other Model Modifications
    • An additional year of FoodNet data (2000) was incorporated, which slightly reduced the total number of predicted cases.
    • Separate mortality to hospitalization ratios were calculated for each sub-population.
    • A 'scaling factor' was selected to adjust each uncertainty distribution of the predicted number of cases to the FoodNet estimates. As a result the 'scaling factor' is a distribution; but the total number of predicted cases for each population is not.
    • The model was rewritten in Visual Basic for Applications to speed up the computation time required for each run of the model and to facilitate review.

Contributors (2003 version)

Team Leader:Richard Whiting, FDA
Risk Assessment Modeler:Clark Carrington, FDA
Project Manager:John Hicks, FDA
Risk Analysis Coordinator:Sherri Dennis, FDA
Scientific Advisor:Robert Buchanan, FDA

Team Members (Section Leads)

Mary Brandt, FDA (Consumption Section Lead)
Anthony D. Hitchins, FDA (Contamination Section Lead)
Richard Raybourne, FDA (Dose-Response Section Lead)
Marianne P. Ross, FDA (Epidemiology Section Lead)

Team Members

John Bowers, FDA
Uday Dessai, FSIS
Eric Ebel, FSIS (formerly)
Sharon Edelson-Mammel, FDA
Dan Gallagher, FSIS (visiting scientist)
Eric Hanson, FDA
Janell Kause, FSIS
Priscilla Levine, FSIS
Wes Long, FDA
Kathy Orloski, FSIS (formerly)
Wayne Schlosser, FSIS
Carol Spease, FDA

Acknowledgments (2003 Version)

The following organizations and individuals are acknowledged for their contributions to this project:

The CFSAN Risk Management Team (lead by John Kvenberg) for advising the risk assessment team.

The Joint Institute for Food Safety and Applied Nutrition (JIFSAN) for sponsoring collection of data on the levels of Listeria monocytogenes in selected ready-to-eat foods.

The National Food Processors Association (Yuhuan Chen, David Gombas, Jenny Scott) for sharing new data on levels of Listeria monocytogenes in selected foods at retail.

Martin Mitchell of the Refrigerated Foods Association, for sharing information on potential growth of Listeria monocytogenes in deli salads.

Shawn Eblen, FDA/CFSAN for sharing research data on growth of Listeria monocytogenes in deli salads.

Randy Hoffman and the American Meat Institute for sharing a survey study on consumer handling of deli meats and frankfurters.

Priscilla Levine, FSIS for providing contamination data for the USDA-regulated foods

The ad hoc Listeria Expert Panel members (Robert Buchanan, Anthony Hitchins, Allan Hogue, Daniel Gallagher, Wallace Garthright, Richard Williams, and Richard Whiting) for providing expert opinion on the weights used to adjust the contamination data.

John Bowers, FDA/CFSAN, for statistical (cluster) analysis of the results.

Kathy Gombas (formerly of FDA/CFSAN) for providing guidance on reorganization of the cheese categories.

The JIFSAN student interns (Louis Thomas, Linda Shasti, Harshita Satija, and Aesha Minter) for assisting with revisions to the contamination database, quality control of tables and figures in this report, and assembling the new references.

Saundra Armstrong of Samari Event and Business Management for professional editing.

Lori Pisciotta, FDA/CFSAN, for assisting with development and refinement of diagrams and tables used in the report and expert technical editing.

Jennifer Cleveland McEntire (visiting scientist) for assisting with the review of the submissions to the public dockets.

Kristen Naschansky Gray (visiting scientist) for assisting with editing the model spreadsheets.

Contributors (2001 Draft Version)

Assessment Team LeadersRichard Whiting, FDA and Wesley Long, FDA
Food ConsumptionMary Bender, FDA (Section Leader)
Eric Hanson, FDA
Lori LeGault, FDA
Nancie McCabe, FDA
Kathy Smith, FDA
Susan Brecher, FDA
Food ContaminationAnthony D. Hitchins, FDA (Section Leader)
MaryLynn Datoc, FDA
Eric Ebel, FSIS
Janell Kause, FSIS
Priscilla Levine, FSIS
Pauline Lerner, FDA
Wayne Schlosser, FSIS
Post-Retail GrowthRichard Whiting, FDA
EpidemiologyPatrick McCarthy, FDA (Section Leader)
John Bryce, FDA
Ruth Etzel, FSIS
Noreen Hynes, FSIS
Kathy Orloski, FSIS
Marianne P. Ross, FDA
Dose-ResponseRichard Raybourne, FDA (Section Leader)
Steve Anderson, FSIS
Wes Long, FDA
Tina Rouse, FDA
ModelingClark Carrington, FDA (Section Leader)
Eric Ebel, FSIS
Mark Walderhaug, FDA
EditingKaren Carson, FDA (Section Leader)
Robert Brackett, FDA
LeeAnne Jackson, FDA
Lauren Posnick, FDA
Tina Rouse, FDA
Scientific AdvisorRobert Buchanan, FDA
Kaye Wachsmuth, FSIS
Assessment CoordinatorSherri Dennis, FDA

Acknowledgments (2001 Draft version)

The following organizations and individuals are acknowledged for their contributions to this project:

Dr. Laurene Mascola, Dr. Udo Buchholz, Dr. Elizabeth Bancroft, and Grace Run, Los Angeles County Department of Health Services and Dr. Richard Ruby, FDA Los Angeles District Office, for retrieving files from the 1985 cheese outbreak and assisting in reanalysis of the data.

Drs. Outi Lyytikäinen, National Public Health Institute, Helsinki, Finland and T. Autio, R. Maijala, P. Ruutu1, T. Honkanen-Buzalski, M. Miettinen, M. Hatakka, J. Mikkola, V. J. Anttila, T. Johansson, L. Rantala, T. Aalto, H. Korkeala, and A. Siitonen for providing information from the 1999 butter outbreak.

Members of the National Advisory Committee on Microbiological Criteria for Foods for twice listening to presentations on the structure and data from the risk assessment and for providing their insight and advice.

Members of the Risk Assessment Consortium for critically reviewing an earlier draft of the risk assessment.

International Dairy Foods Association, for providing data on Listeria monocytogenes levels in pasteurized milk, ice cream, and frozen dairy products.

Drs. Paul Mead, Larry Slutsker, and Stephanie Wong of the Centers for Disease Control and Prevention for providing insight into FoodNet data and its use in this risk assessment.

American Meat Institute for providing information on storage times and temperatures between the manufacturing plant and retail sale for meat products.

Members of the Risk Assessment Reference Team including Sharon Edelson-Mammel, Shawn Eblen, Antonio deJesus, Ann McCarthy, and Carole Shore.

FSIS staff scientists including Walter Hill, Victor Cooke, Gerri Ransom, Priscilla Levine, Carl Custer, and Pat Abraham for their assistance in collecting and analyzing data.

Amy Lando and the Georgetown University Center for Food and Nutrition Policy for sharing their unpublished data.

Peggy Hayes of the Centers for Disease Control and Protection for sharing her original data with FSIS.

Members of the FSIS Meat and Poultry Hotline, including Bessie Berry, Marva Adams, Kathy Bernard, Olga Catter, Gertie Hurley, Marilyn Johnston, Sandy King, Robyn Sadagursky, Diane VanLonkhuyzen, Mary Wenberg, CiCi Williamson, and the Food Safety Education Staff, including Susan Conley, Sandy Facinoli, Barbara O'Brien, for assisting in conducting the consumer survey on frankfurters.