Listeria and listeriosis: what you need to know
Tuesday 13 August 2019
If you’ve ever been pregnant or shared a meal with a mum-to-be, you’re probably aware that a few foods are off the menu. Soft cheeses, deli meats, and pre-prepared salads are just some of the foods that pregnant women should avoid, to reduce the risk of exposure to listeria.
But it’s not just pregnant women who are at increased risk of listeria infection (listeriosis). Older people and people with weakened immune systems are also susceptible. Although uncommon, listeriosis can be devastating; in Australia, it causes around 150 hospitalisations and around 15 deaths each year.
Like other food-borne illnesses, understanding how to avoid exposure to listeria is the best way to stay safe and healthy. We’ve explored what causes listeriosis, who is at greatest risk, and how to reduce your chance of infection.
What is listeria?
Listeria (Listeria monocytogenes) is a type of bacteria that can contaminate food. If you eat food contaminated with listeria, there’s a chance you can become ill with a serious infection called listeriosis. Listeriosis can also be transmitted from a pregnant mother to an unborn baby in the womb or during childbirth.
Listeriosis is a relatively rare illness, even though listeria itself is quite common. Listeria can be found in soil, water, vegetation and sewage; pets and other animals can also carry it. Listeria may also be present in different foods, and it’s by eating contaminated foods that most people fall ill with listeriosis.
People most at risk of listeriosis
Listeriosis is of greatest concern for:
- Pregnant women and their babies
- Newborn babies
- People aged 65 years and over
- People with weakened immune systems, including those with illnesses like cancer and diabetes, and people on medication that can suppress the immune system.
Pregnant women who contract listeriosis may only experience mild symptoms or infection, or even no symptoms at all. Despite this, the risk of transmitting the infection to the unborn baby is high. Listeriosis can pass from mother to baby via the placenta. Unborn babies and newborns have underdeveloped immune systems, which means they are more vulnerable to serious infection. Listeriosis in pregnancy can lead to devastating outcomes including miscarriage, stillbirth, premature birth, or a very ill newborn.
As we age, our immune system function declines. This means that older people are more susceptible to a range of illnesses and infections, including listeriosis and other food-borne illnesses. Similarly, people with weakened immunity are at increased risk because the body’s natural defences against infection-causing bacteria are impaired.
Symptoms and treatment
For most healthy people, exposure to listeria may cause mild symptoms or no symptoms at all. It can take weeks for symptoms to appear after infection.
Symptoms may include:
- Muscle aches and joint pain
If you are at increased risk of listeriosis and experience any symptoms or have potentially been exposed to contaminated foods, it’s very important to speak with a health professional. Prompt treatment with antibiotics can prevent serious complications of listeria infection.
Causes of listeriosis
As listeria is transmitted by eating contaminated foods, the best way to protect yourself against listeriosis is to be aware of high-risk foods, avoid them if you are at an increased risk of infection, and follow good food safety practices.
- Cold meats or chicken, including packaged sliced meats and deli meats
- Raw seafood, such as oysters and sashimi
- Cooked ready-to-eat seafood, such as prawns
- Smoked ready-to-eat seafood, such as smoked salmon
- Pre-prepared and pre-packaged fruit or vegetables, such as from a salad bar or buffet
- Unpasteurised dairy products, such as raw milk
- Soft, semi-soft, or surface-ripened cheeses, including brie, camembert, ricotta, feta, and blue
- Soft-serve ice-cream
- Paté or meat spreads.
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.
If you suspect a potential outbreak of foodborne illness in your area, you can report it to your local public health unit.