Assessing the Risk of Pathogenic Vibrio Species in Tasmanian Oysters
Vibrios are an emerging food safety issue for the Tasmanian and broader Australian shellfish industry. The first reported Australian outbreak of gastrointestinal illness associated with Vibrio parahaemolyticus and local oysters was from Moulting Bay, Tasmania in 2016; followed by further cases reported in WA from oysters sourced from a single jurisdiction outside of state. Data collected following the shellfish related outbreak in Tasmania (FRDC project 2015-042: Assessing the Occurrence of Pathogenic Vibrio Species in Oysters from Moulting Bay) highlighted the risk in Moulting Bay, but also noted the paucity of information on the prevalence of these organisms in Australian bivalve harvest regions. There are no limits set for vibrios in bivalve shellfish under the Food Standards Code. However, the FSANZ Guidelines “Microbiological Examination of Ready-to-Eat Foods” suggests that levels of V. parahaemolyticus in food product 3 cfu/gm are satisfactory, 3-100 cfu/gm are marginally acceptable, 100-10,000 cfu/gm are unsatisfactory and over 10,000 cfu/gm are considered potentially hazardous. The classification under the FSANZ Guideline only considers total number of V. parahaemolyticus and not pathogenic strains, hence using a conservative approach. The Codex Alimentarius Commission Guidelines for the Application of General Principles of Food Hygiene to the Control of Pathogenic Vibrio (CAC/GL 73-2010) includes a separate Annex relating directly to control of these species in bivalve shellfish. The document recommends that monitoring be undertaken in harvest areas for levels of total and potentially pathogenic V. parahaemolyticus (based on the presence of the tdh and trh genes) and V. vulnificus to determine the level of regional and seasonal variation.
Understanding the prevalence of V. paraheamolyticus (total and pathogenic) and V. vulnificus in commercial shellfish and the risk to public health is crucial in providing the Australian bivalve industry and State Shellfish Control Agency the necessary knowledge and tools to mitigate risk to the consumer, ensure product integrity and market access for industry. The current proposal is in response to the nominated RD&E priorities identified by the TASRAC.
Final report
The South Australian Research and Development Institute (SARDI) in collaboration with the Tasmanian oyster industry and regulators, University of Tasmania and Plant and Food Research New Zealand undertook a survey of significant foodborne Vibrio species (Vibrio parahaemolyticus and Vibrio vulnificus) in eleven major commercial Tasmanian shellfish production areas. Surveyed growing areas were selected in consultation with the Tasmanian Shellfish Market Access Program (ShellMAP) and Tasmanian Primary Produce Safety Program to represent a range of production environments and different production practices, as well as various regions with and without prior history of foodborne V. parahaemolyticus illnesses. Commercial Pacific Oysters (Magallana gigas) and Blue Mussels (Mytilus galloprovincialis) were tested for Vibrio levels over three summer/autumn and two winter/spring periods between 2020-2022. Local environmental data, including harvest water and air temperature, rainfall, river flow and salinity, were also collected. The results of the survey have been used to develop the first Australian risk profile for Vibrio, specific to commercial Tasmanian shellfish, and to identify significant environmental drivers of Vibrio risk in individual surveyed harvest areas.
