P-047. Distribution of Vibrio parahaemolyticus and V. vulnificus Levels in U.S. Market Oysters

J. L. Nordstrom1, J. C. Bowers2, J. A. Krantz1, K. R. Calci1, R. Byars3, J. Johnson4, K. Kasturi5, M. Kawalek6, E. Gonzalez5, J. Obando5, J. Versace5, L. Phan6, K. Thammasouk4, S. Eliasberg3, L. Chatman3, J. Welch3, A. DePaola1;
1US FDA/GCSL, Dauphin Island, AL, 2US FDA/CFSAN, College Park, MD, 3US FDA/ORA, Atlanta, GA, 4US FDA/ORA, Bothell, WA, 5US FDA/ORA, Jamaica, NY, 6US FDA/ORA, Irvine, CA.

A year long nationwide retail market study of live oysters was initiated by FDA in January 2007 to determine levels of human pathogens including Vibrio parahaemolyticus (Vp) and V. vulnificus (Vv). The purpose of this study was to assess the accuracy of quantitative risk assessment (QRA) predictions of exposure recently developed by FDA and FAO/WHO and to compare levels of these pathogens to those observed in a similar study conducted in 1998-99. Market oysters were collected bimonthly from nine states and analyzed for the abundance of Vp (total and pathogenic) and Vv using MPN-culture (DNA colony hybridization) and/or MPN-real-time PCR methods. Total Vp and Vv were seasonal in distribution with high levels in the summer (1.3 to 4.4 log Vp/g and -1.3 to 3.8 log Vv /g, depending on the region and method). The highest regional levels of either organism were observed in oysters harvested from states along the Gulf of Mexico and the Mid Atlantic Coasts. Mean levels of pathogenic (tdh and/or trh) Vp were similar in seasonal and regional distribution, as total Vp levels with the highest levels observed from samples collected in the summer from the Gulf and Mid Atlantic. Overall, Vp levels were not significantly different from those observed in the previous market study in 1998-99. The observed levels of Vp agreed well with those predicted in FDA’s Vp Risk Assessment (VPRA) with the notable exception of higher summer levels of total and pathogenic Vp in the Mid Atlantic region. Pathogenic Vp levels were not analyzed in the previous retail study, but the observed levels in this study were in agreement with the QRA predictions. Total Vv levels were lower in all regions, except the Mid Atlantic, as compared to the previous retail study, but were still in general agreement with QRA predictions. Lower levels of Vv in oysters from the Gulf of Mexico in 2007 compared to the 1998-99 study are consistent with the reduction seen in reported Vv illness from some of the Gulf Coast states. The data collected in this study should provide a baseline that can be used to determine the effectiveness of recently adopted controls for reducing exposure of these pathogens to consumers of raw oysters.