What is Listeriosis
Listeriosis, is a rare but serious disease caused by the bacteria Listeria monocytogenes (L. monocytogenes) that can survive and grow on certain high risk foods. While it is probably common for people to eat foods contaminated with a small amount of the bacteria, only some people are at risk of becoming sick. The people who do get sick may require hospitalisation and it may lead to death.
What are the symptoms?
Listeriosis can cause different symptoms depending on which part of the body has been affected and the usual health of the person. Symptoms can include fever, muscle aches, and sometimes nausea and diarrhoea. Infection with L. monocytogenes may also cause septicaemia (blood poisoning) and meningitis (inflammation of the outside of the brain), and death can occur because of these complications.
Pregnant women generally experience mild symptoms themselves; however infections during the pregnancy can lead to miscarriage, stillbirth or infection of the newborn baby.
Symptoms usually start between 3 to 70 days (average 21 days) after eating food contaminated with the bacteria.
How is it spread?
L. monocytogenes is commonly found in the environment (such as soil) and some raw foods. Unlike many other bacteria, L. monocytogenes are unusual because they can grow in the refrigerator. Eating foods that contain L. monocytogenes does not cause illness in most people however some can become sick. Babies can be born with listeriosis if their mothers eat contaminated food during the pregnancy.
Listeriosis does not spread from person-to-person.
Who is at risk?
Eating foods that contain L. monocytogenes does not cause illness in most people. The disease mainly affects the elderly, pregnant women and their unborn and newborn babies, and people with weakened immune systems due to illness or medication (for example, people on cancer treatment or steroids, and people with diabetes, kidney disease, liver disease and HIV infection).
How is it prevented?
Listeriosis can be prevented by avoiding high risk foods and handling food safely.
Avoid high risk foods:
- pre-prepared and pre-packed fruit and vegetable including coleslaw, fresh fruit salad and pre-cut melons
- unwashed fresh fruits (including melons) and vegetables, and drinks made from fresh fruit or vegetables where washing procedures are unknown (excluding canned or pasteurised juices)
- pre-cooked cold chicken
- cold delicatessen meats
- raw or undercooked meat, chicken or seafood
- soft cheeses such as brie, camembert, ricotta or blue-vein (unless cooked and served hot)
- sprouted seeds and raw mushrooms
- ready-to-eat seafood and smoked seafood (for example, smoked salmon)
- pre-prepared sandwiches, wraps and sushi that contain any of the meats, salads or cheeses mentioned above
- unpasteurised milk or milk products
- soft serve ice creams
Handle and store food safely:
- thoroughly cook raw meat, chicken and seafood
- thoroughly cook frozen vegetables
- wash raw vegetables and fruit thoroughly before cutting or eating
- keep raw meat, chicken and seafood separate from all other foods
- use separate knives and cutting boards for different foods - raw meat, unwashed vegetables and ready to eat foods
- wash your hands before, during and after preparing food, going to the toilet, or after handling animals
- wash knives and cutting boards well after preparing uncooked foods
- eat cooked food as soon as possible
The NSW Food Authority provides further information on foods to eat and avoid during pregnancy.
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 for listeriosis involves antibiotics and supportive care. When infection occurs during pregnancy, antibiotics can often prevent infection of the unborn baby or newborn.
Listeria in Australia
While listeriosis can be a very severe illness, the number of cases reported in Australia each year is relatively low, with around 80 cases reported each year. Most people infected with listeriosis are not connected to an outbreak, however outbreaks can occur. Outbreaks caused by listeriosis have been associated with rockmelon, delicatessen meats, raw milk, soft cheeses, pre-prepared salads (for example, from salad bars), unwashed raw vegetables, paté, cold diced chicken and pre-cut fruit and fruit salad.
Preventing the spread of listeria in Australia
Listeriosis is mainly acquired by eating contaminated foods. Food safety standards in Australia are designed to minimise the contamination of food with bacteria including L. monocytogenes. It is difficult to completely remove the risk as this bacteria is so widespread in the environment. Cases of listeriosis are reported to public health authorities so outbreaks can be identified and managed, and particular causes detected.
Talk to your doctor about preventing listeriosis if you are pregnant or if you think you might be at increased risk due to illness or medications.
More information on listeriosis can also be found by contacting your state or territory health department.