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Overseas information: www.cdc.gov/ncidod/diseases/Index.htm

LISTERIA INFECTION - (LISTERIOSIS)

What is Listeria Infection?

Listeria infection or listeriosis, is an illness usually caused by eating food contaminated with bacteria known as Listeria monocytogenes.

Who Is at Risk of Listeria Infection?

Listeria infection can affect people differently.  Healthy people may develop few or no symptoms.  However, for some people, the infection can be serious enough to require hospitalisation and be a threat to life.

People who are at particular risk of infection include:

• Pregnant women and their unborn babies.
• Newborn babies.
• The elderly.
• Anyone whose immune system has been weakened by disease or illness, for example:
  • Cancer
  • Leukaemia
  • Diabetes
• or Liver or kidney disease.
• Anyone on medication such as prednisone or cortisone as this can also suppress the immune system.  This includes organ transplant patients.

What Are the Symptoms?

Healthy people may not be affected at all.  In persons at risk, symptoms may include fever, headache, tiredness, aches and pains.  These symptoms may progress to more serious forms of illness, such as meningitis (brain infection) and septicaemia (blood poisoning).  Less common symptoms are diarrhoea, nausea and abdominal cramps.

In pregnant women, listeria infection is usually a mild illness.  A high temperature before or during labour may be the only sign.  However, even a mild form of the illness can affect the unborn baby (foetus) and can lead to miscarriage, stillbirth, premature birth or a very ill baby at birth.

How Common is Listeria Infection?

Listeria infection is relatively uncommon.  However, the fatality rate amongst at-risk people is high.  In Victoria, between 8 and 24 cases of listeria infection are reported to the Department of Human Services each year.

Can Listeria Infection be Treated?

Yes, listeria infection can be treated successfully with antibiotics if treatment is started early.

Where is Listeria Found?

Listeria bacteria are widespread and commonly found in soil, silage and sewage.  They have also been found in a variety of foods, including raw meat, raw vegetables and some processed foods.  Sometimes, it is not possible to identify which particular food caused a person's illness as symptoms may not appear for 3 to 70 days after eating contaminated food.

Outbreaks of listeria infection due to foods such as soft cheeses, milk, coleslaw and pate have been reported in Europe, North America and Australia.

How Can You Avoid Listeria Infection?

As listeria bacteria are commonly found in the environment, they are impossible to eradicate.  Some exposure to the bacteria is unavoidable.  Most people are, however, at low risk of listeria infection.

• Saying no to high risk foods.
• Good food handling always.
• Avoiding contact with any animal afterbirth (placenta) and with aborted animal foetuses, as listeria infection has been known to cause illness and abortion in animals.

High Risk Foods

These include:

• Ready-to-eat seafood such as smoked fish and smoked mussels.
• Pre-mixed raw vegetable salads, such as coleslaw.
• Pre-cooked meat products which are eaten without further cooking or heating, such as pate, sliced deli meat, and cooked diced chicken (as used in sandwich shops.)
• Any unpasteurised milk or foods made from unpasteurised milk.
• Soft serve ice creams.
• Soft cheeses, such as brie, camambert, ricotta.

Reducing Your Risk of Listeria Infection

Unlike most other food-contaminating bacteria, listeria can grow in the refrigerator.  However, listeria bacteria are readily killed during cooking.  At-risk people can further reduce their risk by:

• Eating only freshly prepared foods.
• Re-heating left-over foods till piping hot.
• Avoiding dips and salad dressing in which vegetables may have been previously dipped.
• Avoiding ready-to-eat foods which have been refrigerated for more than one day.

Safe Foods

These include:

• All freshly cooked foods.
• Hard cheeses, cheese spreads, processed cheese.
• Milk - freshly pasteurised and UHT.
• Yoghurt
• Tinned and pickled food.

Good Food Handling and Storage

Good food handling and safe storage of food are important for everyone.  To anyone at risk of the serious complications of listeria infection, such practices are especially important.  You can reduce the risk of developing listeria infection and other food-borne illnesses, such as gastroenteritis, by following some basic food hygiene and food storage rules:

Wash your hands before preparing food and between handling raw and ready-to-eat foods.

• Keep all food covered.
• Place all cooked food in the refrigerator within one hour of cooking.
• Refrigerate raw meat, raw poultry and raw fish below cooked or ready-to-eat foods to prevent any drip from contaminating these foods.
• Keep your refrigerator clean and the temperature below 5^oC.
• Strictly observe use-by or best-by dates on refrigerated foods.
• Do not handle cooked foods with the same implements (tongs, knives, cutting boards) used on raw foods, unless they have been thoroughly washed with hot soapy waterbetween uses.
• Wash raw vegetables and fruit well before eating.
• Defrost food by placing it on the lower shelves of a refrigerator or use a microwave oven.
• Thoroughly cook all food of animal origin, including eggs.
• Keep hot foods hot (above 60^oC) and cold foods cold (at or below 5^oC).
• Reheat food until the internal temperature of the food reaches at least 70^oC.  (piping hot).

Correct Use of Microwave Oven

If you use a microwave oven, read the manufacturer's instructions carefully and observe the recommended standing times, to ensure the food attains an even temperature before it is eaten.

Any Other Questions?

For further advice, contact your local doctor, community health centre, maternal and child health nurse.  Fact sheets are also available in community languages.

For further information contact the Communicable Diseases Unit, Department of Human Services on Telephone: (03) 9616 7777.

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