title: Quantitative risk assessment of noroviruses in drinking water based on qualitative data in Japan.
abstract: Noroviruses are one of the major causes of viral gastroenteritis in Japan. A quantitative risk assessment was conducted to evaluate the health risk caused by this virus in drinking water. A Monte Carlo analysis was used to calculate both the probability of infection and the disease burden using disability-adjusted life years (DALYs). The concentration of noroviruses in tap water was estimated based on qualitative data and a most probable number (MPN) method with an assumed Poisson lognormal distribution. This numerical method was evaluated using two sets of available count data of Cryptosporidium: that collected from a river and that found in tap water in Japan. The dose-response relationships for noroviruses were estimated using assumed ID50 (10 or 100). The annual risk was higher than the US-EPA acceptable level (10(-4) [infection/ person-year]) but around the WHO level (10(-6) [DALYs/ person-year]). As suggested by others, since microbial concentrations are generally lognormally distributed, the arithmetic mean was directly related to the annual risk, suggesting that the arithmetic mean is more useful in representing the degree of microbial contamination than the geometric mean.
authors.affiliation: Department of Urban Engineering, University of Tokyo, Tokyo, 113-8656, Japan. masago@water.civil.tohoku.ac.jp
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Masago
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Katayama
authors.forename: Toru
authors.initials: T
authors.lastname: Watanabe
authors.forename: Eiji
authors.initials: E
authors.lastname: Haramoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hashimoto
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Omura
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Hirata
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Ohgaki
mesh_terms: D000818:Animals; D003198:Computer Simulation; D003458:Cryptosporidium / Q000235:genetics*; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D007564:Japan; D008962:Models, Theoretical; D009010:Monte Carlo Method; D029322:Norovirus / Q000235:genetics*; D016012:Poisson Distribution; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018570:Risk Assessment; D045483:Rivers; D014871:Water Microbiology; D014881:Water Supply