Listeria

Listeriosis is a rare disease caused by infection with the bacteria Listeria monocytogenes. Listeria is commonly found in soil, water, sewage and the intestinal tracts of animals. Listeriosis can be caused by contact with these sources or eating contaminated foods.

Symptoms

Healthy people exposed to Listeria may not experience any symptoms or only mild symptoms. However, people in certain high-risk groups may develop severe illness.

Symptoms of listeriosis may include:

• fever
• headache
• tiredness
• muscle aches
• less commonly – diarrhoea.

In more severe cases there may be:

• inflammation of the brain (encephalitis)
• the lining of the brain and spinal cord (meningitis)
• blood poisoning (septicaemia).

Pregnant women may experience only mild symptoms, however, listeriosis can lead to miscarriage, premature birth, stillbirth or infection in the newborn.

Who is at risk of infection

Listeriosis can cause severe disease or death for high-risk individuals such as:

• foetuses (unborn babies)
• newborn babies
• elderly people
• people with weakened immune systems, such as those:
  • being treated for cancer
  • on immunosuppressive medications
  • with human immunodeficiency virus (HIV).

How Listeriosis is spread

Listeriosis is most commonly caused by eating contaminated food. It can also occur after contact with animals infected with Listeria. Person-to-person spread does not occur, apart from mother-to-baby transmission during pregnancy or childbirth.

Prevention

Taking a few simple precautions can help prevent listeriosis.

For instance, you should:

• thoroughly cook raw meats such as beef, lamb, pork and chicken
• thoroughly wash raw fruit and vegetables before eating
• separate raw foods from cooked and ready-to-eat foods
• wash hands, knives and cutting boards before and after handling any raw foods and between handling different kinds of foods
• refrigerate perishable foods and eat them as soon as possible
• wash hands after handling animals.

Foods to avoid for high risk people

If you (or someone in your household) have a weakened immune system or are pregnant, the best way to avoid listeriosis is to eat freshly cooked or freshly prepared food.

Try to avoid foods that have a higher risk of Listeria contamination such as:

• cold meats from delicatessen (deli) counters and sandwich bars
• packaged, sliced ready-to-eat meats
• pre-cooked cold ready-to-eat chicken (whole, portions, or diced)
• rockmelon in any form
• any purchased pre-cut or pre-prepared fruit including fruit salads
• uncooked frozen vegetables
• sprouted seeds (such as bean sprouts, alfalfa, etc.)
• pre-prepared or pre-packaged salads, including those from buffets and salad bars
• raw, chilled or smoked seafood, such as raw oysters, sashimi and sushi, smoked salmon, and cooked ready-to-eat prawns
• soft, semi-soft and surface-ripened cheeses such as brie, camembert, ricotta, blue and feta (unless cooked and eaten while hot)
• refrigerated pâté or meat spreads
• soft serve ice cream
• unpasteurised dairy products.

You can further reduce your risk by:

• avoiding food that is past its ‘best before’ or ‘use by’ date
• refrigerating leftovers promptly and using them within 24 hours, or freezing them
• cooking food thoroughly
• reheating food until it is steaming hot.

Incubation period

The time between being exposed to Listeria and developing listeriosis symptoms can vary from 3 to 70 days, but is usually about 3 weeks.

Diagnosis

Listeriosis is generally diagnosed by having blood or other bodily fluid tested for the bacteria.

Treatment

Treatment involves antibiotics and supportive therapy. When infection occurs during pregnancy, antibiotics can prevent infection of the foetus or newborn.

More information

For more information about Listeria or listeriosis, contact:

• your doctor
• the Health Protection Service, Communicable Disease Control Information Line during business hours on (02) 5124 9213.

Listeriosis is a notifiable disease. Cases notified to ACT Health are investigated by Public Health Officers.

Acknowledgements

• Heymann DL, 2015, Control of Communicable Diseases Manual, 19th edition.
• Food Standards Australia New Zealand, Listeria and food - advice for people at risk, 2018.