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). Babies, 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.
What is listeriosis?
Listeriosis is a serious infection in humans caused by the bacteria Listeria monocytogenes. It usually causes only a mild illness but may progress to more serious infection (known as invasive listeriosis), including meningitis.
It's 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.
Listeriosis is primarily a foodborne disease transmitted by ingestion of contaminated food such as ready-to-eat processed meats (for example, packaged or freshly deli-sliced meats like ham and salami), soft cheeses, pre-prepared salads, raw vegetables, pate and shellfish.
People most at risk
Listeriosis is of greatest concern for:
- pregnant women and their babies
- newborn babies
- people aged 65 years and over
- people with weakened immune systems, such as those who are:
- HIV positive
- transplant patients
- have illnesses such as cancer and diabetes
- have a history of alcohol abuse
- 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 defenses 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:
- fever
- headache
- tiredness
- muscle aches and joint pain
- nausea
- vomiting
- diarrhoea
- neck stiffness.
Symptoms may appear within 24 hours of eating contaminated food, but it can take up to two months for symptoms to develop.
For vulnerable people, listeriosis can lead to life-threatening conditions such as meningitis (infection of the lining of the brain) and sepsis.
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.
If you are concerned that you may have listeriosis, please see your GP immediately.
If in doubt, always call Triple Zero (000).
Prevention
As listeria is most often 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.
Foods at higher risk of listeria contamination include:
- 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
- rockmelon
- 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
- pâté or meat spreads.
You can further reduce your risk by:
- cooking food thoroughly, especially meat, poultry and fish
- washing fruits and vegetables thoroughly before eating
- avoiding soft cheeses, such as camembert and brie, and pâté
- avoiding pre-prepared salads and meats
- keeping raw meat, poultry and fish separate from other foods in the refrigerator and freezer
- cleaning and disinfecting all surfaces that come into contact with raw meat, poultry and fish
- washing your hands thoroughly after handling raw meat, poultry and fish
- avoiding food that is past its best before or use-by date
- refrigerating leftovers promptly and using them within 24 hours, or freezing them
- 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.
More information
- Listeria | Queensland Government
- Listeria | Food Standards Australia New Zealand
- Listeria | Pregnancy, Birth and Baby
- Food poisoning and foodborne illnesses
- Food recalls
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