Infectious dose/dose response: The infectious dose is unknown but presumed to be low (FDA 2003).
Levels in seafood: Norovirus has been shown to accumulate in bivalve molluscs and is commonly isolated from oysters grown waters impacted by faecal contamination (Formiga-Cruz et al. 2002; LeGuyader et al. 2000). Of particular concern, a study by Schwab et al. (1998) demonstrated that depuration of oysters may result in only a limited reduction of Norovirus concentration (7% reduction following 48 h depuration, compared with 95% reduction of bacteria).
