March 2, 2018


What is listeria and how does it spread in rockmelons? Ten cases have been reported so far, including three deaths.

Vincent Ho, Western Sydney University

Three people have now died after eating rockmelon (cantaloupe) contaminated with listeria. A total of ten cases have been confirmed in New South Wales, Queensland and Victoria between January 17 and February 9, and more are expected.

Listeriosis is caused by eating food contaminated with a bacterium called Listeria monocytogenes. It’s an uncommon illness but can be deadly if it causes septicaemia (blood poisoning) or meningitis (inflammation of the membranes around the brain).

The ten reported cases are among people aged over 65. The elderly are particularly susceptible to listeriosis, as are pregnant women and their fetuses, and those with weakened immune systems.

Past outbreaks have been linked with raw milk, soft cheeses, salads, unwashed raw vegetables, cold diced chicken, pre-cut fruit and fruit salad.

Read more:
Understanding the recent listeria-linked cheese recall

How does it spread?

Listeria is found widely in soil, water and vegetation, and can be carried by pets and wild animals.

A vegetable or fruit food product can become contaminated anywhere along the chain of food production: planting, harvesting, packing, distribution, preparation and serving.

Even on a farm, sources of contamination can include irrigated waters, wash waters and soil. Listeria can survive for up to 84 days in some soils.

Heavy rains on a crop can splash listeria from soils onto the surface or skin of the vegetable, especially those that grow low to the ground, such as rockmelons.

Read more:
Scary berries: how food gets contaminated and what to do

Listeria contamination can also occur in restaurants and home kitchens, where the bacterium can be found – and spread – in areas where foods are being handled.

Listeria monocytogenes is quite a hardy bacterium. It can survive at refrigerated temperatures and has adapted mechanisms to survive acidic environments such as the stomach.

What are the symptoms?

First, it’s important to note that eating foods that contain listeria bacteria won’t necessarily make you sick.

Listeria monocytogenes can survive in the body, moving between cells (human phagocytes) for a long time. This is, in part, why there can be a long “incubation period” between ingestion and onset of illness. This can be as long as 70 days but is usually around three weeks.

Symptoms include fever, muscle aches and gastrointestinal problems such as nausea, vomiting and diarrhoea.

In severe cases, symptoms can include collapse and shock, particularly if there is septicaemia. If the infection has spread to the central nervous system, more worrying symptoms will occur, such as headache, stiff neck, confusion, seizures and the person may go into a coma. In such cases, the fatality rate is as high as 30%.

In pregnant women, the bacteria are thought to cross the lining of maternal blood vessels and then enter the fetal circulation of the placenta. Infection during pregnancy can lead to miscarriage, stillbirth and newborn infections.

Treatment for confirmed infections involves antibiotics and supportive measures such as intravenous fluids for dehydration.

When infection does occur in pregnancy, the early use of antibiotics can often prevent infection of the fetus or newborn.

But even with very prompt treatment, infections can be deadly in high-risk groups.

Why are some groups at higher risk?

Pregnant women are a special group known to be at higher risk for listeriosis. The underlying mechanisms for why pregnant women are susceptible to listeriosis are not well understood but it’s thought an altered immune system is involved.

Read more:
How to keep school lunches safe in the heat

People with weakened immune systems, such as those on cancer treatment or medications that suppress the immune system, are more susceptible to developing listeriosis because their bodies are less able to fight off the bug.

Newborn babies are also extremely vulnerable as their immune systems have not yet matured, as are the elderly, whose immune systems are declining.

Tracking and finding the source

The life cycle of the bacteria can make it difficult to track the source of the outbreak. Listeria is able to contaminate a variety of foods, which may have a long shelf life, and listeriosis has a long incubation period.

All ten people in the current outbreak consumed rockmelon before they fell sick and state and territory health departments were able to pinpoint the source to a farm in the NSW Riverina district.

But it’s not always that easy. The current South African listeriosis outbreak is the worst outbreak in recorded history with 172 deaths recorded to date. The source has not yet been identified.

Read more:
How we can prevent more Listeria deaths

How can you prevent listeriosis?

Here are some practical things you can do to prevent the spread of listeria:

  • thoroughly cook raw food from animal sources, such as beef, lamb, pork and poultry
  • wash raw vegetables and fruit thoroughly before eating
  • use separate cutting boards for raw meat and foods that are ready to eat
  • wash your hands with soapy water before and after preparing food
  • wash knives and cutting boards after handling uncooked foods
  • wash your hands after handling animals.

If you are at greater risk for listeriosis, consider avoiding:

  • pre-cut melons such as rockmelon or watermelon
  • pre-packed cold salads including coleslaw and fresh fruit salad
  • pre-cooked cold chicken, cold delicatessen meats, pâté
  • raw and uncooked smoked seafood (such as smoked salmon)
  • unpasteurised milk or milk products, soft cheeses (such as brie, camembert, ricotta or blue-vein)
  • sprouted seeds
  • raw mushrooms.

The ConversationThe NSW Food Authority is also advising consumers who are most at risk of listeriosis to avoid eating rockmelon and discard any rockmelon they already have at home.

UPDATE at 6pm on 2 March

Sadly a third death has been confirmed this afternoon.

Victoria’s deputy chief health officer said five Victorians had been infected, and that one of those people had died after being hospitalised.

Dr Brett Sutton confirmed the victim had been diagnosed with listeriosis and subsequent testing linked them to the outbreak strain.

Dr Sutton would not provide the age or gender of the victim.

The Victorian cases range in age from 65 to 88, and included three men and two women.

Vincent Ho, Senior Lecturer and clinical academic gastroenterologist, Western Sydney University

This article was originally published on The Conversation. Read the original article.

Read more:

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  • Scary that healthy eating can make you sick.


  • This is very worrying indeed, I have gone off rockmelons now.


  • Thanks for the information MOM. It is very timely as I was wondering why my husband was told not to eat rockmelon. He has been diagnosed with incurable cancer which had spread throughout his body. Anything I can do to keep him around for as long as possible is very helpful.


  • I always buy whole rockmelons, but nonetheless threw mine out once I knew there was a problem. Washing this fruit is useless really as no-one eats the skin, it’s usually peeled during preparation. So how does this virus get into the fruit?


  • Thanks for the information mom.
    I’m so glade our family has gone away from buying packet foods as much as we possibly can.
    If we do purchase something in big amounts like watermelon (rather than a cut up piece) we will freeze some of it and eat at a later date.
    I hope that everyone who suffered from this has a speedy recovery


  • Such a fact filled article. One of my favourite fruits but I don’t think I’ll be buying any for a couple of weeks yet, just to be sure


  • Thank you for this well researched and written article. Very informative and a bit scary!


  • This is really concerning as there is such a move to pre-packed fruits, salads, vegetables, etc. It has certainly put me off rockmelon for the near future. I think I’ll leave it alone for the rest of the season.


  • This is a very informative article that everyone should read. Thanks for posting it.


  • we got an email and I just through out what was left of ours just in case – the only person who had eaten any was my eldest daughter.

    It’s such a shame that this has happened and that people have died because of it.


  • I received an email from Coles that I should return the rock melon I bought several weeks ago (as if we wouldn’t eaten that one yet) and that I could get my money back if I hand over the receipt (yeah, who would keep all their receipts for several weeks ?) !!

    • We bought a rock melon too – but it turned quickly and we did not eat it. It was unusual because it turned so quickly.

      • I keep receipts just till the beginning of the following month, when the bank statement arrives and I check it against the receipts.

      • Excellent method for keeping receipts!


  • The ways to prevent it makes sense, wash everything! And good advice about not buying pre-cut melons too. More importantly keep a healthy immune system by eating lots of fresh organic fruit and veg preferable home grown. Most people will fight the bacteria if you have an abundance of good bacteria in your body, so don’t feed the bad ones with processed dead food. Grow your own sprouts too. Heaps of fun for kids to do.


  • I knew about listeria, but this is the first time I’ve seen it linked to fruit.


  • So tragic that people have died from consuming rockmelon. :(


  • Very scary. Everyone I know gives their kids rock melon.

    • I heard there has been an issue with watermelon in the past too. Good hygiene is essential at all times. It is important that food be kept at the correct temperature. At restruants, cafes etc hot food must be kept at 60c or higher – that is regulation


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