Listeria is a food-borne bacteria that can make you sick. Infection with listeria bacteria is called listeriosis. In healthy adults and tamariki listeria usually causes few or no symptoms. But some people are more at risk of severe disease.

Symptoms of listeriosis

In most people, listeriosis has no symptoms or only causes mild symptoms for a few days, such as:

  • fever
  • muscle aches
  • feeling sick (nausea) or throwing up (vomiting)
  • runny poos (diarrhoea).

Symptoms usually start between 3 to 70 days (5 weeks) after eating contaminated food. The average time for symptoms is 21 days.

Complications of listeriosis

Listeriosis is particularly dangerous for pregnant people. Pregnant people generally experience mild symptoms themselves. But infections during the pregnancy can lead to:

  • miscarriage
  • premature labour
  • stillbirth
  • infection of newborn pēpi.

Who is at risk of severe disease

People who are more at risk include:

  • pregnant people and their unborn pēpi
  • newborn pēpi
  • people with weakened immune systems
  • older people who have a loss of physical, mental, or social ability.

People with weakened immune systems include people who:

  • have cancer
  • have diabetes
  • have liver or kidney disease
  • are taking immunosuppressive treatments.

How listeriosis spreads

Listeriosis is spread when raw meat, unpasteurised milk, raw fruit and vegetables are contaminated with the bacteria. If you eat contaminated food you may get listeriosis.

Diagnosing listeriosis

If you think you have listeriosis visit your healthcare provider. They can do blood tests, and other tests to confirm if you have it.

Treating listeriosis

Most people have mild symptoms and can look after themselves at home.

If you more unwell you may need antibiotics.

If you are pregnant, antibiotics can often prevent infection of your unborn pēpi or newborn.

If you are not sure what to do call Healthline on 0800 611 116

Preventing listeriosis

Some foods are more likely to be contaminated. People who are at risk of severe disease should not eat them.

Foods that are unsafe for people at risk of severe infection include:

  • chilled seafood like 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 and using them within 24 hours, or freezing them
  • cooking food all the way through
  • reheating food until it is steaming hot.

Clinical review

This content was written by HealthInfo clinical advisers. It has been adapted for Health Information and Services.

Clinical advisers — HealthInfo (external link)