U. S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
January 2001

Draft Risk Assessment on the Public Health Impact of
Vibrio parahaemolyticus in Raw Molluscan Shellfish

CONTRIBUTORS

The Vibrio parahaemolyticus risk assessment was performed and this document prepared by the following task force members:

Team Leaders
Marianne Miliotis, William Watkins

Harvest
Marleen Wekell (Lead)
Atin Datta, Elisa Elliot, Walter Hill, Charles Kaysner, Brett Podoski

Post Harvest
Angelo DePaola, David Cook (Co-leads)
George Hoskin, Susan McCarthy, William Watkins

Public Health
John Bowers (Lead)

Epidemiology
Marianne Ross (Segment lead)
Karl Klontz, Debra Street, Babgaleh Timbo

Consumption
Michael DiNovi

Dose-Response
Donald Burr (Segment lead)
John Bowers, Mahendra Kothary, Wesley Long, Marianne Miliotis,
Ben Tall, Mark Walderhaug

Modeling
John Bowers (Lead), Mark Walderhaug

ACKNOWLEDGEMENTS

The V. parahaemolyticus Task Force greatly appreciates the efforts of all the following people in providing us with comments, information and assistance we needed to accomplish this risk assessment:

The Task Force would especially like to thank the FDA/CFSAN Offices and Risk Assessment Consortium members for intensive review of the document in December, as well as Federal employees from other agencies, and Special Government Experts, for review of the document in May. We are also deeply grateful to Lauren Posnick for her outstanding contribution in preparing the interpretive summary of this document, Carolyn Jeletic for excellent technical editing of this document, and Faye Feldstein for assisting with assembling all the references.

COMMENTS AND INFORMATION REQUESTED DURING PUBLIC COMMENT PERIOD

The Food and Drug Administration has always committed itself to bringing the best science available to all of its decisions and activities, which is the underlying reason that this and other quantitative microbial risk assessments are undertaken. As with any risk assessment, the knowledge available for the conduct of the current risk assessment was incomplete and assumptions had to be made when specific data were lacking or limited in scope. When such assumptions were made, we have attempted to seek the best scientific information available including having all assumptions and modeling approaches reviewed by the National Advisory Committee on Microbiological Criteria for Foods and the interagency Risk Assessment Consortium. However, to ensure that we have both identified all key data sources and submitted the assessment to a rigorous peer review, we are releasing the assessment in draft form. A comment period has been established during which we will be actively seeki suggestions, and additional data sources. Written comments should be submitted to the Dockets Management Branch (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Room 1061, Rockville, MD 20852 within 60 days after publication of the document. Two copies of comments are to be submitted, except that individuals may submit one copy. Comments must be identified with the Federal Register Docket No. 99N-1075. Some of the key areas that we are seeking comments are listed below. The information acquired during the comment period will be reviewed and used, as appropriate, to further enhance the risk assessment and decrease uncertainty to the greatest degree possible. As stated in the Federal Register, Docket No. 99N-1075, the preliminary results of the draft V. parahaemolyticus risk assessment will be presented at a public meeting during the comment period.

Examples of specific assumptions made in the risk assessment for which we are seeking comments and additional data include:

• Pathogenesis was based on the presence of the most characterized virulence factor of the organism, thermostable direct hemolysin (TDH). Based on the levels from the literature, levels of pathogenic V. parahaemolyticus used ranged from 1.6% to 6.4% for the West Coast; 0.1% to 0.4% remaining regions.

• Time after harvest to refrigeration was based on a 1997 GCSL survey that included dealer reported statistics on the length of harvest , as well as on the NSSP time-temperature control plan.

• All V. parahaemolyticus in oysters, regardless of pathogenicity, have similar growth and survival rates.

• The growth rate of V. parahaemolyticus in oysters is approximately 1/4 that of the growth rate in broth at all environmental temperatures.

• Lag time to growth of V. parahaemolyticus in oyster after harvest is negligible.

• The growth rate of V. parahaemolyticus drops uniformly down to zero during the period of initial refrigeration following harvest.

• Depuration is ineffective against V. parahaemolyticus in oysters.

• Equal consumption patterns were assumed between immune compromised and healthy populations.

• Equal virulence was assumed for all pathogenic V. parahaemolyticus.

• The dose-response relation was shifted by 1 log₁₀ from that based on published clinical trials, in order to achieve a relationship that was more reflective of the CDC disease estimates.

The FDA is also seeking comments on the appropriateness of the risk assessment model and the parameters used to develop the model.

• Preliminary modeling of the Harvest Module did not show a great effect of salinity on the levels of pathogenic V. parahaemolyticus, within the range that oysters are normally harvested. Therefore this parameter was not included in our simulations.

• The study by DePaola et al., 1990. (Reference number 38) was deemed to be most appropriate for the purpose of this risk assessment, because this study was the most inclusive of seasonal changes in V. parahaemolyticus density in oysters from major oyster producing areas representative of the Pacific, Gulf and Atlantic Coasts. Are there other studies that should have been considered?

Hypertext updated by bap/kwg/dms 2001-JAN-30