LISTERIOSIS

Last updated: 30 January 2008

What is listeriosis?

Listeriosis is a rare illness caused by eating food contaminated with bacteria called Listeria monocytogenes. The Listeria bacteria are common in soil 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), meningitis (inflammation of the brain) and miscarriage in pregnant women. 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. Infection during pregnancy can lead to miscarriage, stillbirth and infection of the newborn.

How is it spread?

Listeria monocytogenes is 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. Outbreaks of illness have been associated with raw or contaminated milk, soft cheeses, preprepared salads (for example, from salad bars), unwashed raw vegetables, and ready to eat meat such as paté. 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.

Who is at risk?

Pregnant women, newborns, the elderly and people with weakened immune systems (for example: people on cancer treatment or steroids and people with AIDS).

How is it prevented?

To prevent listeriosis:

• 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)
• avoid unpasteurised milk or foods made from unpasteurised milk (for example, soft cheeses)
• 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:

• pre-packed salads
• pre-cut fruit
• pre-cooked chicken
• meats
• delicatessen meats
• paté
• raw seafood
• smoked fish
• unpasteurised milk or milk products
• soft cheeses such as brie, camembert, ricotta, or blue-vein
• sprouted seeds and raw mushrooms

How is it diagnosed?

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

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 or 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.

Updates and other links:

• Having a baby  /pubs/2006/having_a_baby.html
• Pregnancy and food safety  http://www.foodauthority.nsw.gov.au/consumer/pregnancy.asp
• FSANZ Listeria Advice  http://www.foodstandards.gov.au/foodmatters/listeria/index.cfm
• PHU perinatal investigation form  /resources/publichealth/infectious/diseases/listeriosis_perinatal_questionnaire_pdf.asp
• PHU non-perinatal investigation form  /resources/publichealth/infectious/diseases/listeriosis_non-perinatal_questionnaire_pdf.asp