Listeriosis is a type of food poisoning caused by eating foods contaminated with Listeria bacteria. While it’s not always dangerous, it can cause serious problems for some people.

What is listeria and listeriosis?

Listeria (full name Listeria monocytogenes) is the name of a type of bacteria. If you get infected by this bacteria, you can get an illness called listeriosis.

Listeria bacteria are widespread in the environment. However, the illness listeriosis is not common — in Australia, only about 150 people are hospitalised because of listeriosis each year.

Infection with Listeria bacteria doesn’t usually cause illness in healthy people. However, certain groups of people are at greater risk of getting listeriosis, including:

• pregnant women and their babies
• people who have a weakened immune system due to illnesses such as cancer, diabetes or chronic infections
• people over the age of 65
• people on medication that can suppress the immune system (such as prednisone or cortisone)

Listeriosis can be life threatening for some people.

What causes listeriosis?

Most people who get sick with listeriosis have eaten food contaminated with Listeria.

Some foods are more likely to be contaminated by Listeria than others. These are called ‘high-risk foods’ and include:

• unpasteurised dairy products, such as raw milk
• soft-serve ice-cream
• soft cheeses such as brie, camembert, ricotta, blue and feta
• raw seafood such as oysters, or cooked ready-to-eat seafood
• pre-prepared fruit or vegetables, such as from a salad bar
• rockmelon
• unwashed raw vegetables
• paté or meat spreads
• cold meats or chicken, including packaged sliced meats

Although Listeria bacteria are easily killed by heat, cooked foods can get contaminated if you don’t use good hygiene when handling or storing them. Listeria can even grow in refrigerated food, if you keep it there too long.

You can also get listeriosis from contact with infected farm animals, although this is rare.

What are the symptoms of listeriosis?

People who are healthy can get listeriosis and not even know it, or they may have developed mild ‘flu' or gastroenteritis-like symptoms. However, people with a weakened immune system can get a much more severe illness.

Listeriosis can take weeks or even months to develop, and may be quite mild at first.

Symptoms can include:

• fever
• muscle aches
• headache
• tiredness
• aches and pains
• nausea
• vomiting
• diarrhoea
• discoloured urine
• abdominal cramps

Some people get a severe infection and can have a stiff neck, confusion, loss of balance, collapse, convulsions and coma. A few people die of listeriosis each year.

How is listeriosis diagnosed?

A diagnosis of listeriosis is made by growing Listeria bacteria from a sample of blood, spinal fluid or, in pregnant women, the placenta.

How is listeriosis treated?

Listeriosis can be treated with antibiotics. If you are diagnosed when pregnant, treatment can often stop your child getting infected.

Can listeriosis be prevented?

To help prevent yourself from getting listeriosis, you can:

• avoid eating high-risk foods (see ‘Causes’, above)
• avoid food that has passed its ‘use by’ date
• eat only freshly prepared food
• prepare food carefully — cook it thoroughly or re-heat until steaming
• store leftovers in the fridge and eat them within 24 hours
• use good food hygiene (such as washing your hands before preparing food)

See more tips about food safety here.

When to see a doctor

If you think you could have listeriosis, see your doctor. If you are pregnant, this is urgent because even though you may only have mild symptoms, your unborn baby could get seriously ill.

More information

• Try the healthdirect Symptom checker and Question builder .
• Visit Food Standards Australia & New Zealand.