Listeria are bacteria that can cause a serious illness called listeriosis in some people. While listeria infection is uncommon and causes few or no symptoms in healthy people, it can be very dangerous for those people at risk.

Listeriosis is usually caused by eating food contaminated by certain types of listeria bacteria. The listeria bacteria are found widely in nature. Storing contaminated foods, even in the refrigerator, may allow the listeria bacteria to grow.

The bacteria may be present in raw foods or may contaminate food after it has been cooked or processed.

Soft and surface-ripened chesses are high-risk foods for listeriosis. Photo: Lisa Maree Williams

High risk listeria foods are:

Ready-to-eat cold meats

Cold cooked chicken

Pre-made salads, fruit salads

Pate

Raw and chilled ready-to-eat seafood

Soft and surface-ripened cheese

Soft serve ice-cream

Unpasteurised dairy products

Pregnant women are at high risk of listeriosis. Photo: Getty Images

Those at high risk of listeriosis:

Pregnant women and their unborn children

Older people, generally those over 65 years

People of all ages whose immune systems have been weakened by disease or illness such as cancer, leukaemia, AIDS, diabetes, liver or kidney disease.

Anyone on medication that can suppress the immune system, for example prednisone or cortisone, including organ transplant patients.


What are the symptoms?

In persons at risk, symptoms may include fever, headache, tiredness, aches and pains. Less common symptoms are diarrhoea, nausea and abdominal cramps. Symptoms may progress to more serious forms of the illness, such as meningitis and septicaemia.

Symptoms in pregnant women may be mild, but listeriosis can result in miscarriage, premature birth or, in rare cases, stillbirth.

Beware of salad bars if you're at risk of listeriosis.

What precautions should I take if I am at risk?

Eat only freshly cooked food and well-washed freshly prepared fruit and vegetables. However, leftovers can be eaten if they are refrigerated promptly and kept no longer than a day.

Do not eat food if there is any doubt about its hygienic preparation or storage.

Cook foods thoroughly. Thorough cooking of food kills Listeria bacteria.

Reheat foods to 'steaming' hot

If planning to eat previously cooked and refrigerated leftovers, only keep them in the refrigerator for a day and reheat them thoroughly to steaming hot. This will kill listeria bacteria.

When reheating food, especially in a microwave, make sure the food is steaming hot throughout.

Avoid ready-to-eat food from salad bars, sandwich bars, delicatessens and smorgasboards.

Avoid foods that are past their 'best before' or 'use by' date.

Only buy ready-to-eat hot food if it's steaming hot.

If eating out, order hot meals.

Wash hands thoroughly before preparing food.

Food hygiene steps to reduce the risk of food borne disease.

Thoroughly wash and dry hands before preparing food, particularly before preparing ready-to-eat food.

Keep refrigerator clean and operate it below 5 degrees.

Wash knives, cutting boards and kitchen appliances and dry thoroughly after handling raw food to prevent contamination of cooked and ready-to-eat foods.

Thoroughly wash and dry raw fruit and vegetables before eating or juicing.

Thaw ready-to-eat frozen food in the refrigerator or microwave – don't thaw at room temperature.

Thoroughly cook all raw meat, chicken and fish.

Don't leave foods to cool on the bench or stove top. Put them in the refrigerator after the steam has gone.

If you are keeping food hot, keep it very hot: 60 degrees or hotter. Keep cold food cold: 5 degrees or colder.

Keep stored foods covered.

Store raw meat separately from cooked and ready-to-eat food in the refrigerator. Store it below other foods so that there is no chance it will drip onto other foods.

When cooking meat, don't underdo it!