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?
If you (or someone in your household) have a weakened immune system or are pregnant, the best way to avoid L. monocytogenes is to eat freshly cooked or freshly prepared food.
Try to avoid foods that have a higher risk of L. monocytogenes contamination such as:
- chilled seafood such as raw oysters, sashimi and sushi, smoked ready-to-eat seafood and cooked ready-to-eat prawns
- cold meats from delicatessen counters and sandwich bars, and packaged, sliced ready-to-eat meats
- cold cooked ready-to-eat chicken (whole, portions, or diced)
- pre-prepared or pre-packaged fruit or vegetable salads, including those from buffets and salad bars
- soft, semi-soft and surface-ripened cheeses such as brie, camembert, ricotta, blue and feta
- refrigerated paté or meat spreads
- soft serve ice cream
- unpasteurised dairy products
- raw mushrooms.
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.
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.