Trading Standards Institute Advice

Food borne illness and contamination: Listeria and listeriosis

This leaflet is for all food businesses, including those involved in food preparation and production, catering businesses, retail premises, restaurants, pubs, cafes, and take takeaway and fast-food shops.

What is Listeria?
Listeriosis is the name given to the illness caused by eating food contaminated with Listeria monocytogenes bacteria. The bacteria are found in soil and water.

Who is at risk?
Listeria bacteria may affect healthy adults and children. However, the disease is particularly dangerous for:

  • pregnant women
  • babies
  • adults with weakened immune systems
  • elderly people, who seem to be becoming more prone to the infection

Where does Listeria come from?
Animals can carry the bacteria and can contaminate foods such as meat and dairy products. Vegetables can become contaminated from the soil they grow in or from manure used as fertilizer. Listeria bacteria may be found in chilled or delicatessen products.

Unpasteurised milk or food made from unpasteurised milk may be contaminated. Products such as soft cheeses and cold meats may become contaminated after processing.

What are the symptoms caused by Listeria
The bacteria may not cause symptoms in the body for up to 70 days after someone has eaten infected food. When symptoms do develop, they may include fever, aching muscles, nausea (feeling sick) and diarrhoea.

These bacteria can affect the nervous system, leading to loss of balance and meningitis. Many pregnant women may feel only a mild, flu-like illness but this can still lead to miscarriage or premature birth.

What do I need to do to control listeria?
Listeria bacteria can multiply in temperatures from as low as -1°C up to 42°C. Because of this, Listeria can grow at temperatures normally found in your fridge, and this makes Listeria a dangerous bacteria to deal with. Listeria is killed by cooking and by heat treatments such as pasteurisation. If there is a problem in the food-production process, some ready-to-eat food may be contaminated after cooking but before packaging.

Listeriosis can be avoided by maintaining high standards of hygiene when producing food:

  • thoroughly cook foods to a core temperature of 75°C (the temperature in the middle at the thickest part)
  • if you are serving raw vegetables, make sure you wash them thoroughly
  • avoid cross-contamination:
    - wash your hands, knives and cutting boards after handling uncooked food  and
    - keep cooked meats separate from vegetables and from all ready-to-eat food
  • keep to use-by dates of chilled foods and serve perishable food (food that goes off quickly) and ready-to-eat food as soon as possible
  • make sure cold processed meats are thoroughly reheated before serving to your customers
  • avoid using unpasteurised milk or food made from unpasteurised milk
  • make sure you continue to thoroughly clean and disinfect your food business premises and food areas

Advice for pregnant women and other people at risk of infection with Listeria
Your customers who fall into the groups of people at risk (see 'Who is at risk?' above) may want to avoid the high-risk foods that are most likely to carry the infection. They should:

  • follow the guidelines above when preparing and serving food
  • not eat cold-stored processed meats, unless they are meant to be reheated and they are reheated thoroughly
  • avoid meat spreads and pate
  • avoid Brie, Camembert and other soft cheeses unless they are made from pasteurised milk
  • avoid eating smoked seafood unless it is to be used in a cooked dish

More information
You will find further guidance in our other leaflets on this website. Information can also be found on the Food Standards Agency (opens in a new window) website.

Alternatively, contact your local environmental health service for advice.

Please note
This leaflet is not an authoritative interpretation of the law and is intended only for guidance.

© 2017 itsa Ltd.