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What is listeriosis?

Listeriosis is a rare disease caused by the bacteria Listeria monocytogenes.

People at higher risk of Listeriosis include pregnant women, new born babies, the elderly and those with weak immune systems. People with weak immune systems include those with cancer, leukaemia, AIDS, diabetes, liver or kidney disease or those on corticosteroid medication.

Listeriosis can be very dangerous for those people at higher risk.

There are only a small number of cases reported in Tasmania each year. Although rare, listeriosis does have a high death rate.

What are the symptoms?

Infections may cause septicaemia (blood poisoning) and meningitis. It can cause miscarriage in pregnant woman.

Symptoms include fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea and diarrhoea. If infection causes meningitis, symptoms include headaches, neck stiffness, confusion, loss of balance, decreased alertness and coma.

Some infected people may have mild gastroenteritis symptoms only. Others may have no symptoms at all. Pregnant women may have relatively mild symptoms then make a quick recovery. However, they may transfer the infection to their unborn child who may be stillborn or born very ill.

The incubation period varies fromthree to 70 days, with the average being about three weeks. Recent studies suggest the incubation period for pregnant people is longer than that for non-pregnant people.

How is it spread?

Listeria bacteria can be widespread in the environment and can be carried by animals (both wild and domestic). Raw meat, unpasteurised milk, raw fruit and vegetables can become contaminated with the Listeria bacteria.

People who are at risk can become infected if they eat food contaminated with the Listeria bacteria. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy.

The main way in which Listeria infection is spread is by eating contaminated foods. Foods associated with the spread of Listeria include unpasteurised dairy products, soft cheeses, raw vegetables, shellfish, raw fish and processed meats such as pâté. Contact with infected farm animals, particularly stillborn animals, can also spread the infection.

Infected people may carry Listeria in their faeces for several months after infection.

How is it diagnosed?

The diagnosis is usually made by growing the bacteria from a sample of cerebral spinal fluid (fluid from around the spinal cord), blood or from samples taken from the baby.

How is it treated?

Listeriosis can be treated successfully if treatment is started early. Admission to hospital is usually necessary and antibiotic therapy is given.

Even with prompt treatment, listeriosis can sometimes result in death. This is more likely in older adults and in people with other serious medical problems.

How is it prevented?

Listeria bacteria are common in the environment and are impossible to remove and some exposure to the bacteria is unavoidable. Most people are at low risk of infection but pregnant women, the elderly and people with weak immune systems should take special care to avoid high risk foods which may be contaminated with Listeria.

High risk foods:

  • pre-cut melons such as rockmelon and watermelon.
  • ready to eat seafood (smoked fish, mussels, oysters) or raw seafood (sushi, sashimi)
  • pre-prepared or stored salads (coleslaw, fresh fruit salad)
  • drinks made from fresh fruit and vegetables where washing procedures are unknown (exceptions are  pasteurised or canned juices)
  • precooked meats which are eaten without further cooking (pate, sliced deli meats such as ham, salami, and cooked diced chicken)
  • any unpasteurised milk or unpasteurised milk products
  • soft cheeses such as brie, camembert, ricotta and feta (these are safe if cooked and served hot)
  • soft serve ice-creams
  • dips and salad dressings in which raw vegetables may have been dipped
  • raw vegetable garnishes
  • sprouted seeds or raw mushrooms

All meat should be properly cooked and only pasteurised dairy products eaten. Raw vegetables should be thoroughly washed before eating.

Detailed advice about Listeria and food for people at risk is available from the Food Standards Australia and New Zealand website

General information on food safety in pregnancy is also available from the Public Health Services website

Pregnant women and people with weak immune systems should avoid contact with sick or stillborn farm animals.

There is no vaccine to prevent listeriosis.

What should I do if I have had contact with someone who has listeriosis?

Passing the Listeria bacteria from one person to another is not common, with the exception of mother to foetus during pregnancy. It is usually acquired from eating contaminated food. If you have had contact with someone with listeriosis you are not at risk of becoming ill from Listeria from contact with that person.

What should I do if I have listeriosis?

If you are more at risk of listeriosis, have eaten high risk foods and experience symptoms which are suggestive of possible Listeria infection, seek medical attention and discuss the foods that have been eaten.

If you have eaten a food that has been recalled due to Listeria contamination and have symptoms, seek medical attention and mention your possible exposure. If you have eaten the food and have no symptoms, no tests are probably required.

Call the Public Health Hotline – Tasmania on 1800 671 738 to speak to a Clinical Nurse Consultant.

1 March 2018