What is listeriosis?

Listeriosis is a rare illness caused by eating food contaminated with bacteria called Listeria monocytogenes. The Listeria bacteria are common in the environment and some raw foods. Eating foods that contain Listeria bacteria does not cause illness in most people. There are typically 20 to 30 cases of listeriosis reported each year in NSW. Although listeriosis is rare, it has a high death rate.

What are the symptoms?

The incubation period (between infection and symptoms) can vary from three to 70 days but on average is about three weeks. Infections may cause septicaemia (blood poisoning) and meningitis (inflammation of the brain). Infection during pregnancy can lead to miscarriage, stillbirth and infection of the newborn.

Symptoms include: fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea and diarrhoea. In the more severe form, symptoms also include collapse and shock. If infection spreads to the central nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, convulsions and coma can occur. About a third of these patients may die.

How is it spread?

Listeria are widespread throughout nature, being commonly carried by many species of both domestic and wild animals. Raw meat, unpasteurised milk, raw fruit and vegetables can be contaminated with the bacteria. People who are at risk can contract listeriosis through eating food contaminated with the Listeria bacteria. Babies can be born with listeriosis if their mothers eat contaminated food during the pregnancy. Outbreaks of illness have been associated with raw milk, soft cheeses, pre-prepared salads (for example, from salad bars), unwashed raw vegetables, paté, cold diced chicken, rockmelon and pre-cut fruit and fruit salad.

Who is at risk?

Pregnant women and the foetus, newborns, the elderly and people with weakened immune systems (for example: people on cancer treatment or steroids, and people with diabetes, kidney disease, liver disease and HIV infection).

How is it prevented?

To prevent listeriosis:

• avoid high risk foods (as described below)
• thoroughly cook raw food from animal sources, such as beef, lamb, pork, or poultry
• wash raw vegetables and fruit thoroughly before eating
• keep raw meat separate from vegetables, cooked foods, and ready- to-eat foods (that is, do not allow the blood from raw meat to come into contact with other food)
• use separate cutting boards for raw meat and foods that are ready to eat (for example, cooked foods and salads)
• wash your hands before and after preparing food
• wash knives and cutting boards after handling uncooked foods
• wash your hands after handling animals
• perishable foods should be stored in a cold (less than 5 degrees Celsius) refrigerator and be washed and eaten as soon as possible.

People at increased risk of listeriosis should not eat:

• rockmelon
• pre-cut fruit or pre-prepared fruit, including fruit salad (pre-packaged, from buffets or from salad bars)
• pre-packed cold salads, including coleslaw (pre-packaged, from buffets or from salad bars)
• frozen vegetables, unless cooked
• pre-cooked cold chicken (whole, portions or diced)
• cold delicatessen meats (freshly sliced, pre-packaged or from sandwich bars)
• paté or meat spreads
• raw seafood
• smoked seafood (for example, smoked salmon), unless cooked and served hot
• chilled seafood (for example, ready-to-eat prawns)
• unpasteurised milk or milk products
• soft cheeses such as brie, camembert, ricotta, or blue-vein (unless cooked and eaten while hot)
• soft serve ice cream
• sprouted seeds

How is it diagnosed?

The diagnosis of listeriosis can be confirmed by blood or other tests requested by a doctor.

How is it treated?

Treatment involves antibiotics and supportive therapy. When infection occurs during pregnancy, antibiotics can often prevent infection of the foetus or newborn. Even with prompt treatment, some infections result in the death of the patient, particularly in the elderly and in people who have other serious medical problems.

What is the public health response?

• Laboratories must notify cases of listeriosis to the local public health unit.
• Public health unit staff may interview the doctor and patient (or family) to find out how the infection occurred.
• The NSW Food Authority, in collaboration with NSW Health, is responsible for the environmental investigation of listeriosis.
• If you are at risk of listeriosis and have questions you should contact your health care provider or local public health unit.

Other links

• Having a baby
• Pregnancy and food safety
• FSANZ Listeria Advice

For further information please call your local Public Health Unit on 1300 066 055.