An outbreak of listeriosis has taken place in New South Wales with an unexpected increase in cases in January and February. Listeria monocytogenes has been found on a number of rockmelons from a NSW supplier. While the link between the farm and the illness cases is not yet conclusive, there is sufficient circumstantial evidence to warn at-risk consumers not to consume rockmelon. At least 10 people have become infected including three deaths. All cases are people in high risk groups, which includes those who are older, pregnant or have underlying health conditions.
Listeriosis is due to consuming food contaminated with Listeria monocytogenes. Listeria is a bacteria that survives and grows on a number of foods including rockmelon, vegetable salads and fruit salads, cold meats, raw seafood, soft cheeses, seed sprouts and others.
Q: Who is investigating the outbreak?
A: NSW Health and the NSW Food Authority are investigating this outbreak. Rockmelons (and other foods) have been implicated in listeriosis outbreaks in Australia and internationally and were naturally a high priority in the investigation. There are many ‘types’ of Listeria monocytogenes and for the outbreak to be linked to a particular food, the DNA finger print of the pathogen must be the same as the Listeria associated with the illnesses and the food. This link has not been confirmed but New South Wales Food Authority has advised this afternoon that there is sufficient information to issue general advice to the elderly and immunocompromised to avoid consuming any rockmelons they have purchased.
A number of retailers have withdrawn rockmelons from retail sale as a precaution.
Q: How does Listeria contaminate fresh produce?
A: Listeria is a bacteria that is found in the environment, in soil and water and in some animals. It is a hardy bacteria that can thrive in food processing and packing plants if not controlled and can survive refrigeration. Listeria is killed by heat, such as from cooking and pasteurization.
Fresh produce such as vegetables and rockmelons are grown in the same environment as Listeria is present. Environmental conditions mean that Listeria has difficulty multiplying to large numbers in the field but it does persist. The rough surface of the rind (skin) of rockmelons provides an ideal place for Listeria to survive, particularly if the fruit is injured as a consequence of rain and irrigation water splash. Listeria bacteria can multiply rapidly if the produce is not thoroughly washed and the wash water is not sanitized.
Produce can also become contaminated from Listeria that is surviving on food contact surfaces such as cracks and joins in steel, on belts, brushes and rollers, and on packaging.
Q: Where is the best place to go for specific information on Listeria and listeriosis?
PMA A-NZ will continue to engage with relevant bodies including the NSW Food Authority, Australian Melon Association and other stakeholders and will provide further information when it comes to hand.
For consumers: Food Standards Australia New Zealand: Listeria and food - advice for people at risk
For industry: Fresh Produce Safety Centre A-NZ: Guidelines for Fresh Produce Food Safety
For further enquiries related to this Fact Sheet
Richard Bennett, Head of Food Safety & Technology, PMA A-NZ
+61 429 329 731
The information in this document is correct as at 27th February 2018