Listeria

What is listeria?

Listeria monocytogenes (listeria) is a foodborne bacteria that causes an illness called listeriosis. Cases of listeriosis are rare, however, they can be a particular concern because the bacteria are able to grow at low temperatures. In healthy adults and children listeria usually causes few or no symptoms.   

However, in rare cases, listeriosis can result in a serious illness called invasive listeriosis. This can lead to conditions such as meningitis or sepsis, and if pregnant, miscarriage or stillbirth.  

You can find information on the symptoms of listeria and how it makes you ill on the following sites:

• NHS - Listeriosis
• NIDirect - Listeriosis
• NHS 111 Wales - Listeriosis
• UKHSA's collection on Listeria: guidance, data and analysis

Important

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

Video: FSA explains listeria

People who are at higher risk of listeriosis

Some people are at a higher risk of listeriosis. The following people can have a weakened immune system, which means they are more susceptible to infection: 

• 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   

Listeria-risky foods

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 washing 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  
• pâté  
• smoked and cured fish – including sushi  
• cooked shellfish  
• soft mould-ripened cheeses – such as camembert, brie, and blue-veined cheeses  
• raw drinking milk (unpasteurised milk)
• products made from raw milk/unpasteurised milk such as cheese or butter  
• pre-prepared sandwiches and salads  
• pre-cut fruits (for example, pre-packed melon slices)  

Although it's less common, you can also catch listeriosis from close contact with farm animals – especially sheep and cows that are giving birth 

How you can reduce the risk of listeriosis at home

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

• chill your food below 5°C - this will stop or significantly slow the growth of bacteria including Listeria 
• refrigerate foods as soon as possible after purchase and eat ready-to-eat foods shortly after removing them from the fridge, within 4 hours or within 2 hours on a very warm day and keep them out of direct sunlight 
• 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, and ready to eat foods provided on the label. If there are no instructions, use opened foods within two days.    
• follow the cooking instructions on the packaging when applicable, and cook or reheat foods (including frozen vegetables) until they are steaming hot right through 
• avoid cross-contamination which might lead to bacteria passing from raw foods to foods that are ready to eat via things like reusable shopping bags, knives, dirty surfaces and chopping boards  
• wash fruit, vegetables and salad leaves thoroughly before eating raw 
• make sure that food preparation areas are clean to prevent harmful bacteria from spreading 
• 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.

England, Northern Ireland and Wales

PDF

View Reducing the risk of vulnerable groups contracting listeriosis as PDF(Open in a new window) (414.13 KB)