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Consumers – Listeria, cooking and food

Listeria bacteria can be found in food

Listeria monocytogenes (referred to as Listeria) are bacteria that can cause a serious illness called listeriosis. Listeria bacteria are found widely in nature and can be transmitted through food. Ready-to-eat products, such as deli meats and salads, cooked poultry products, smoked seafoods, soft cheeses and foods with a long refrigerated shelf life are often linked to outbreaks of Listeria. Once food is contaminated with Listeria the bacteria multiply quickly, even at the recommended refrigeration temperatures of 2 - 4ºC.

People most at risk of developing listeriosis

While listeriosis is uncommon it can be dangerous for some groups, and these people are much more likely to suffer severe effects of the illness. People more at risk of developing the invasive infection include pregnant women and their unborn children; newborn babies; the frail elderly; anyone whose immune system has been weakened by disease or illness, for example cancer, leukaemia, AIDS, diabetes, liver and kidney disease; and anyone on medication that suppresses the immune system.

Symptoms of listeriosis

There are two forms of foodborne listeriosis: non-invasive and invasive.

Non-invasive: symptoms include diarrhoea, fever, muscle pain, headache, occasional abdominal cramps and vomiting. Most people recover fully.

Invasive: for people at risk, listeriosis causes ‘flu-like’ symptoms of fever, headache, diarrhoea, vomiting. In a small number of cases symptoms may progress to more serious forms of the illness, such as meningitis and blood poisoning. In pregnant women symptoms may be mild but can result in miscarriage, premature birth, or in rare cases, stillbirth.

If you think you might have listeriosis, consult a doctor immediately. The illness can usually be diagnosed through a blood test.

Symptoms usually appear within two to 30 days of eating contaminated food, but it can take up to 70 days before people experience symptoms.

Listeriosis is a notifiable disease and cases are reported by doctors to your local public health unit for further investigation.

Top tips to keep your family and friends safe

People at a higher risk of getting listeriosis can reduce the risk of infection by only eating foods that are freshly prepared and well washed, avoiding raw milk products and processed meats, following good hygiene practices and cooking foods thoroughly to kill any Listeria bacteria. Leftovers should be refrigerated immediately and should not be kept for more than two days. Reheated food should be piping hot (over 70ºC) before eating. If you are eating out, choose food that is steaming hot and freshly prepared.

• 4Cs rule – clean, cook, cover, chill [NZ Foodsafe Partnership]

• 20+20 hand washing rule before and after handling food [NZ Foodsafe Partnership]

• Top tips to keep food safe

Related links

Listeria educational resources

Journal articles about Listeria

Listeria – information for commercial cooks and chefs, industry, scientists and media

Last updated 25 March 2009