Risk Analysis, Vol. 30, No. 12, 2010 DOI: 10.1111/j.1539-6924.2010.01444.x Quantitative Risk Assessment of Vibrio parahaemolyticus in Finfish: A Model of Raw Horse Mackerel Consumption in Japan Jun’ichiro Iwahori, 1, * Akio Yamamoto, 2 Hodaka Suzuki, 3 Takehisa Yamamoto, 4 Toshiyuki Tsutsui, 4 Keiko Motoyama, 5 Mikiko Sawada, 5 Tomoki Matsushita, 6 Atsushi Hasegawa, 6 Ken Osaka, 7 Hajime Toyofuku, 8 and Fumiko Kasuga 3 The aim of this study was to evaluate the effects of implemented control measures to re- duce illness induced by Vibrio parahaemolyticus (V. parahaemolyticus) in horse mackerel (Trachurus japonicus), seafood that is commonly consumed raw in Japan. On the basis of currently available experimental and survey data, we constructed a quantitative risk model of V. parahaemolyticus in horse mackerel from harvest to consumption. In particular, the fol- lowing factors were evaluated: bacterial growth at all stages, effects of washing the fish body and storage water, and bacterial transfer from the fish surface, gills, and intestine to fillets during preparation. New parameters of the beta-Poisson dose-response model were deter- mined from all human feeding trials, some of which have been used for risk assessment by the U.S. Food and Drug Administration (USFDA). The probability of illness caused by V. parahaemolyticus was estimated using both the USFDA dose-response parameters and our parameters for each selected pathway of scenario alternatives: washing whole fish at land- ing, storage in contaminated water, high temperature during transportation, and washing fish during preparation. The last scenario (washing fish during preparation) was the most effective for reducing the risk of illness by about a factor of 10 compared to no washing at this stage. Risk of illness increased by 50% by exposure to increased temperature during transportation, according to our assumptions of duration and temperature. The other two scenarios did not significantly affect risk. The choice of dose-response parameters was not critical for evalua- tion of control measures. KEY WORDS: Dose-response model; food-borne microbial disease; quantitative risk assessment; raw fish; Vibrio parahaemolyticus 1 Kochi Medical School, Nankoku, Kochi, Japan. 2 Infectious Disease Research Division, Hyogo Prefectural Insti- tute of Public Health and Consumer Sciences, Kobe, Japan. 3 National Institute of Health Sciences, Setagaya-ku, Tokyo, Japan. 4 National Institute of Animal Health, Tsukuba, Ibaraki, Japan. 5 Business Consulting Department, Hitachi East Japan Solutions, Ltd., Kawasaki, Japan. 6 Mitsubishi Research Institute, Inc., Chiyoda-ku, Tokyo, Japan. 7 Graduate School of Dentistry, Tohoku University, Sendai, Japan. 8 National Institute of Public Health, Wako-shi, Saitama, Japan. ∗ Address correspondence to Jun’ichiro Iwahori, Kochi Medical School, Okohcho-Kohasu, Nankoku, Kochi 783-8505, Japan; tel: +81-88-880-2276; fax: +81-88-880-2278; iwahorij@kochi-u.ac.jp. 1. INTRODUCTION Vibrio parahaemolyticus (V. parahaemolyticus) is a bacterium that is found in marine life and water during the warm season. The consumption of food contaminated with V. parahaemolyticus strains car- rying either the tdh or trh gene, or both, are thought to cause human gastroenteritis. It was reported that about 12,000 patients were infected with V. para- haemolyticus in Japan during 1998, but these annual cases have recently decreased to 1,000–3,000. (1) 1817 0272-4332/10/0100-1817$22.00/1 C  2010 Society for Risk Analysis