Listeria is a group of bacteria found widely in nature e.g. in soil, water and the intestines of many domestic and wild animals, fish and birds. Listeria can survive for long periods of time in soil, leaf litter, sewage, silage, vegetation and water. Listeria is frequently found in food processing environments and has the ability to form biofilms and survive on apparently smooth surfaces.

Listeria infection does not normally affect healthy adults and children. However, it can be very serious for pregnant women and their unborn children, new born babies, the elderly and persons whose immune systems have been weakened by disease or illness, such as those suffering from cancer, leukaemia, AIDS, diabetes, liver or kidney disease and anyone on medication that can suppress the immune system (e.g. corticosteroids such as prednisone or cortisone – but not topical creams and ointments), including organ transplant patients.

All freshly cooked seafood is safe.  Use immediately and store any leftovers in the fridge for consumption within one day.

Fish and shellfish may be potential sources of Listeria, due to their harvest from natural environments where the bacteria can be found. However, it is more likely that Listeria may enter seafood products during and/or after processing through poor hygiene or manufacturing practices, or from subsequent handling of product. This is a special concern for those products that receive minimal or no heat treatment before consumption.

Raw (uncooked) seafood.

Smoked salmon and trout: Smoked salmon and smoked trout have a pH in excess of 6.0 and are usually salted to achieve an aqueous salt content of 3.5%. If Listeria is present in these products it is capable of significant growth, as they have a long shelf life. These products should be avoided by at-risk groups.

Live oysters and mussels: Listeria is rarely isolated from fresh live oysters and mussels, however contamination can occur due to contaminated processing environments. Smoked mussels have been associated with cases of listeriosis in Australia and New Zealand. Pre-opened raw and smoked oysters and mussels should be avoided by at-risk groups.

Peeled prawns (cooked): Peeled prawns (cooked) can be extensively handled both at retail and post-retail, thereby increasing the possibility of contamination. In addition, poor temperature control of retail chilling cabinets may allow the growth of Listeria if present.  Cooked peeled prawns in prawn cocktails, as sandwich fillings, or in pre-made saladshould be avoided, due to the extensive handling of these products and possible time/temperature abuse during storage.

Please contact the NSW Food Authority on 1300 552 406 or your health professional.