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.
What is Listeria?
Listeria monocytogenes is a bacterium that causes listeriosis in humans. This infection can have severe consequences for particular groups of the population.
It can cause miscarriages in pregnant women and be fatal in immunocompromised individuals and the elderly.
How do you contract listeriosis?
By consuming food that has been contaminated with Listeria monocytogenes such as rockmelon, vegetable salads and fruit salads, cold meats, raw seafood, soft cheeses, seed sprouts and other foods.
How does Listeria contaminate fresh produce?
Listeria is a bacteria that is found in the environment, in soil and water and in some animals. It is 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.
Listeria has difficulty multiplying to large numbers in the field but it persists in moist environments and at low temperature.
The rough surface of the rind (skin) of rockmelons provides an ideal place for Listeria to survive, particularly if the fruit is damaged or as a consequence of rain and irrigation water splash.
Listeria bacteria can multiply rapidly on produce after harvest that is not thoroughly washed and the wash water is not sanitized.
Produce can also become contaminated with Listeria that is surviving on food contact surfaces such as cracks and joins in steel, on belts, brushes and rollers, and on packaging that comes into contact with the produce.
Investigation of the outbreak
Queensland Health is working with the New South Wales Food Authority to investigate this matter further.
Advice for consumers
As a precaution, consumers particularly those who are elderly, pregnant or immune compromised who may have rockmelon already in their home are advised to discard it.
The following links contain more information about Listeria and listeriosis: