Listeria is a foodborne bacterium that can make you sick. Infection with listeria bacteria is called listeriosis. In healthy adults and children listeria usually causes few or no symptoms, but some people are more at risk of severe disease.
Who is at risk of severe disease?
People who are more at risk include:
- pregnant women and their unborn babies
- newborn babies
- people with weakened immune systems (including cancer patients, diabetics, people taking immunosuppressive treatments, people with liver or kidney disease
- frail older people.
Listeriosis is particularly dangerous for pregnant women. It can cause miscarriage, premature labour or stillbirth, and can cause infection in their baby.
Listeria and food safety
Food safety procedures aim to prevent listeria getting into foods we eat. Some foods are more likely to be contaminated so people who are at risk of severe disease should not eat them.
Foods that are unsafe for people at risk of severe infection include:
- uncooked, smoked or ready-to-eat fish or seafood, including oysters, prawns, smoked ready-to-eat fish, sashimi or sushi
- paté, hummus and tahini-based dips and spreads
- cold pre-cooked chicken
- processed meats including ham and all other chilled pre-cooked meat products including chicken, salami and other fermented or dried sausages*
- pre-prepared, pre-packaged or stored salads (including fruit salads) and coleslaws
- raw (unpasteurised) milk and any food that contains unpasteurised milk*
- soft-serve ice creams
- soft, semi-soft or surface-ripened soft cheese (eg, brie, camembert, feta, ricotta, roquefort).*
* Note that the foods on this list are safe to eat if heated thoroughly to steaming hot (ie, above 72°C) where appropriate.
In most people, listeriosis has no symptoms or only causes mild symptoms for a few days, such as
- muscle aches
- nausea (feeling sick) or vomiting
Pregnant women generally experience mild symptoms themselves; however infections during the pregnancy can lead to miscarriage, stillbirth or infection of the newborn baby.
Symptoms usually start between 3 to 70 days (average 21 days) after eating food contaminated with the bacteria.
Most people have mild symptoms and can look after themselves at home.
If people need treatment, they may get antibiotics and supportive care. When infection occurs during pregnancy, antibiotics can often prevent infection of the unborn baby or newborn.
Call Healthline 0800 611 116 if you are unsure what you should do.
If you (or someone in your household) have a weakened immune system or are pregnant, the best way to avoid listeria is to eat freshly cooked or freshly prepared food.
Try to avoid foods that have a higher risk of contamination such as:
- chilled seafood such as raw oysters, sashimi and sushi, smoked ready-to-eat seafood and cooked ready-to-eat prawns
- cold meats from delicatessen counters and sandwich bars, and packaged, sliced ready-to-eat meats
- pre-prepared or pre-packaged fruit or vegetable salads, including those from buffets and salad bars
- soft, semi-soft and surface-ripened cheeses such as brie, camembert, ricotta, blue and feta
- refrigerated paté or meat spreads
- soft serve ice cream
- unpasteurised dairy products
- raw mushrooms.
You can further reduce your risk by:
- avoiding food that is past its best before or use by date
- refrigerating leftovers promptly and using them within 24 hours, or freezing them
- cooking food thoroughly
- reheating food until it is steaming hot.
Safer food choices
For comprehensive information on food safety for people with low immunity refer to the Ministry for Primary Industries guide: Pullout guide to food safety with low immunity (PDF, 784 KB).