Infective dose/dose response: The infective dose is usually generally high at >105 cells, but can be lower when the food vehicle is a fatty or buffering substance allowing passage through the acidic environment of the stomach (Jay et al. 1997). As few as 15–20 cells may also cause illness depending upon age and health of host and strain differences (FDA 2003).
Levels in seafood: Farmed seafood, or seafood harvested from in-shore waters, estuaries or rivers may be contaminated with Salmonella spp. due to faecal pollution of surrounding waters. Fish caught in deep waters are more likely to become contaminated with Salmonella spp. after harvesting (Jay et al. 2003), rather than from their growing environment. The prevalence of salmonellae in shrimp has been reported at 8.1 per cent from a survey of 211 samples (Gecan et al. 1994).
Epidemiological data: In 2002, 7917 cases of salmonellosis were reported in Australia, which represented a rate of 40.3 cases per 100,000 population (OzFoodNet 2003). During 1995–2002, there were five reported outbreaks associated with consumption of contaminated seafood including oysters, cooked prawns and crayfish (Appendix 2; Food Science Australia & Minter Ellison Consulting 2002).
Outbreaks have also occurred internationally due to the consumption of contaminated seafood. For example, smoked fish (halibut) was implicated in 11 cases of salmonellosis with S. Paratyphi in Germany in 1991 (Kuhn et al. 1994), and 19 cases of salmonellosis was due to the consumption of cockles contaminated with S. Enteritidis in the United Kingdom (Greenwood et al. 1998).
