Listeria

What is listeria?  

Listeria monocytogenes (listeria) is a foodborne bacterium that causes an illness called listeriosis. Cases of listeriosis are rare, and in healthy adults and children listeria usually causes few or no symptoms. However, some people have a higher risk of becoming ill and developing severe illness (invasive listeriosis).   

Important

There is specific advice on eating ready-to-eat cold smoked fish for people who have a higher risk of becoming ill with listeriosis.

Video: FSA explains listeria

People who are at higher risk of listeriosis 

• pregnant women and their unborn babies - listeriosis infection can cause stillbirth or miscarriage, or sepsis or meningitis in new-born babies 
• those with weakened immune systems, including (people with certain underlying conditions such as  cancer, diabetes, liver and kidney disease), or anyone taking medications which can weaken the immune system  
• older people have an increased risk compared with the general population, and this risk increases with age  

Foods that can be contaminated with listeria  

Although listeria is widespread in the environment and can contaminate a wide range of foods, it is more common in ready-to-eat foods. Ready-to-eat foods are foods which are intended to be eaten without further preparation, such as heating or cooking. Food businesses are required to apply food safety controls to make sure listeria is not present at unsafe levels in these foods. Examples of ready-to-eat foods are:   

• cold pre-cooked meats – such as chicken  
• deli meats – such as salami and cold cuts  
• smoked and cured fish – including sushi  
• cooked shellfish  
• soft mould-ripened cheeses – such as camembert, brie, and blue-veined cheeses  
• pâté  
• unpasteurised milk, or products made from unpasteurised milk  
• pre-prepared sandwiches and salads  
• pre-cut fruits (for example, pre-packed melon slices)  

Steps to reduce the risk  

To reduce the risk of listeriosis, it’s important to:  

• keep foods cold until you are ready to eat them - make sure your fridge temperature is set at 5°C or below.  
• refrigerate foods as soon as possible after purchase   
• eat ready-to-eat foods within four hours of removing them from the fridge   
• always eat, cook or freeze foods by their use-by date. Foods after their use-by date may look and smell fine, but they could be unsafe and make you ill. You cannot see, smell or taste bacteria that causes foodborne illness.  
• always follow the storage instructions, including those for opened foods, provided on the label. If there are no instructions, use opened foods within two days.   
• keep raw and ready-to-eat foods separate to avoid cross-contamination  
• follow the cooking instructions on packaging when applicable, and cook or reheat foods (including frozen vegetables) until they are steaming hot right through  
• wash your hands regularly with soap and water before, during and after meal preparation   

Smoked fish advice for higher risk groups  

Pregnant women or people who have a weakened immune system are more likely to suffer severe symptoms from listeria infection and are advised to avoid eating ready-to-eat cold-smoked or cured fish products, such as smoked salmon or gravlax.   

As the risk of serious illness from listeriosis increases with age, older people should also be aware of the risk of eating cold-smoked and cured fish and consider taking steps to reduce listeria infection. These steps include eating foods before the use by dates, ensuring the product is kept refrigerated (below 5°C) or considering using the safer alternatives below. 

Ready-to-eat cold smoked fish is normally labelled as ‘smoked’ fish on its packaging. It has been cured (for example in salt) and then smoked at a low temperature, but it is not cooked through. Ready-to-eat cold smoked fish typically comes in thin slices, as shown in the image on this page. Examples include smoked trout slices and smoked salmon slices.    

Ready to eat cold-smoked or cured salmon is thinly sliced. The slices are an orange, pink or red colour and will feel slightly moist to touch.   

Safer alternatives for those at higher risk of listeria infection include: 

• cooked smoked fish - this can be in dishes such as quiche, fish cakes, pie or gratin:  
  • cooking will kill any listeria that may be present  
  • if you are cooking smoked fish yourself, make sure it is steaming hot all the way through and served or chilled immediately. Cooked smoked fish may be served cold after being chilled in the fridge  
  • care should be taken with adding cold-smoked or cured fish to dishes like cooked pasta or scrambled eggs. Cook the fish first as warming it through as you prepare your meal will not heat the fish to a high enough temperature to kill listeria.   
• tinned/canned smoked fish  
• thoroughly cooked fish fillets (fresh or frozen)

Video: listeria in smoked fish 

FSA explains: foodborne bacteria  

Foodborne bacteria live in the gut of many farm animals. During rearing, slaughter and processing it can be transferred into:  

• meat  
• eggs  
• poultry  
• milk  

Other foods like green vegetables, fruit and shellfish can become contaminated through contact with animal and human faeces. For example, from manure used to improve soil fertility or sewage in water.  

Foodborne bacteria can be spread by cross-contamination. For example, if raw and cooked foods are stored together, bacteria can spread from the raw food to the cooked food.  

Some foodborne bacteria can also be spread from pets to people and from person to person through poor hygiene. This includes things like failing to wash your hands properly after going to the toilet or after handling pets.  

Advice for healthcare and social care organisations

We have developed guidance for healthcare and social care organisations to help protect people within their care from contracting listeriosis.