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Listeria and food

Listeria – what it is

Listeria monocytogenes is a bacteria that can cause a serious illness called listeriosis. While listeriosis is uncommon and causes few or no symptoms in healthy people, it can be very dangerous for some groups, and these people are much more likely to suffer severe effects of the illness.

Listeria is widely found in nature and it can be transferred through food. Ready-to-eat products, such as deli meats and salads, soft cheeses and foods with a long refrigerated shelf life are often associated with the bacteria. Once food is contaminated with Listeria the bacteria multiply quickly, even at recommended refrigeration temperatures (2–4°C).

Managing Listeria by making safer food choices

Listeria is managed by hygienic preparation, storage and handling of food. Information on proper food handling is on the NZFSA website

People most at risk from Listeria

Although listeriosis is uncommon it can be very dangerous. 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 Listeria

In people 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 blood poisoning. In pregnant women symptoms may be mild, but the consequences can be severe as listeriosis can result in miscarriage, premature birth or, in rare cases, stillbirth. If you think you might have listeriosis, consult a doctor who can usually diagnose the illness through a blood test.

Listeriosis in New Zealand

In New Zealand around 25 cases occur annually. Of those about 20% are associated with pregnancy or newborn babies. Between 5 and 7% of people affected by the disease die a year on average. The number of cases recorded here is similar to that found in countries with similar health status.

Precautions for at-risk people

If you or anyone in your household is in a risk group, you can reduce the likelihood of infection by taking certain precautions. Eat only foods that are freshly prepared and well washed, follow good food hygiene practices such as washing and drying hands, and cook foods thoroughly to kill any Listeria bacteria. Refrigerate leftovers immediately and do not keep for more than two days. Reheat to steaming hot (over 70°C) before eating.

Higher risk foods

Choose safe foods

Ready-to-eat foods from delicatessens and smorgasbords should be avoided as they may have been prepared some time before being displayed, allowing time for Listeria bacteria to grow on them. Also avoid processed meats and soft cheeses unless they have been cooked until steaming hot. Only eat take-away food that is steaming hot and freshly prepared, such as pizza or fish and chips, and always choose from the hot options when dining out.

Safer alternatives to high risk foods

*If these products are purchased in the primary producer’s original packaging, small quantities can be eaten immediately after opening. Do not reseal and eat later, and do not eat if they have been repackaged in a deli or supermarket as they may have been contaminated with pathogens.

Updated March 2009