Listeriosis

Listeriosis is an infection that usually develops after eating food contaminated by listeria bacteria.

In most people, listeriosis is mild and causes symptoms including a high temperature (fever), vomiting and diarrhoea. These symptoms usually pass within three days without the need for treatment.

However, in rare cases, the infection can be more severe and spread to other parts of your body, causing serious complications, such as meningitis. Common signs of severe listeriosis include a stiff neck, severe headache and tremors.

Where is listeria found?

Listeria bacteria have been found in a range of chilled "ready-to-eat" foods, including:

pre-packed sandwiches
pâté
butter
soft cheeses – such as Brie or Camembert, or others with a similar rind
soft blue cheese
cooked sliced meats
smoked salmon

The bacteria may also be passed on through contact with the stools of infected animals or human carriers.

Seeking medical help

If you're pregnant and show signs of listeriosis, or if you have a young child who shows signs of the illness, seek immediate medical advice.

If you're not pregnant and are an otherwise healthy adult, seek medical help if your symptoms are severe.

Listeriosis is usually diagnosed with a blood test. If it's thought that the infection has spread to the nervous system, further tests may include an MRI scan and a lumbar puncture.

Mild cases of listeriosis usually don't need treatment. However, if the infection has spread to the nervous system, you'll need to be treated with antibiotics in hospital for several weeks.

Preventing listeriosis

The best way to reduce your chances of developing listeriosis is to ensure you always practise good food hygiene. For example, you should:

not use food past its "use by" date
follow storage instructions on food labels
make sure that the temperature of your fridge is 0C to 5C
cook food thoroughly

If you're in a high risk group for listeriosis – for example, if you're pregnant or you have a weakened immune system, avoid eating some foods, such as soft mould-ripened cheese or pâté.

'At-risk' groups

Some people are particularly vulnerable to severe listeriosis.
This includes:

people over 65 years of age
pregnant women and their unborn babies
babies less than one month old

Listeriosis and pregnancy

Pregnant women are at particular risk of developing listeriosis. This is because the body's natural defences against the listeria bacteria are weaker during pregnancy.

Pregnant women are almost 20 times more likely to develop listeriosis compared with the rest of the population.

A listeria infection in pregnancy doesn't usually pose a serious threat to the mother’s health. However, it can cause pregnancy and birth complications, and can result in miscarriage.

Symptoms

Symptoms of listeriosis in most healthy adults are mild. They usually develop from 3-70 days after the initial infection.

Symptoms are similar to flu and gastroenteritis, and include:

a high temperature (fever) of 38C (100.4F) or above
muscle ache or pain
chills
feeling or being sick
diarrhoea

These symptoms usually pass within a few days, even without treatment.

Severe listeriosis

If the infection spreads into the blood (septicaemia) or the central nervous system (invasive listeriosis), the symptoms of fever, muscle pain and chills tend to be severe.

If the infection spreads to the nervous system and the brain, additional symptoms can include:

severe headache
stiff neck
changes in mental state, such as confusion
seizures (fits)
lack of physical co-ordination
uncontrollable shaking or twitching (tremor)

If listeriosis spreads to the brain, it can cause meningitis.

Listeriosis in infants

Symptoms of listeriosis in infants can include:

lack of interest in feeding
irritability
seizures
breathing difficulties, such as rapid breathing or grunting when breathing
skin rash
a higher or lower temperature than normal

The normal body temperature for a baby is around 37C (98.6F). Read about high temperatures in children.

When to seek medical help

You should seek immediate medical help if:

you show signs of severe listeriosis
your child shows signs of listeriosis
you're pregnant with a fever and chills

If you need help outside normal surgery hours, contact your local out-of-hours service.

Causes

Listeriosis is caused by a type of bacteria called listeria. It's mainly spread through contaminated food.

Listeria is widespread throughout the environment and can be found in soil, wood, decaying vegetation and water.

Contaminated food

Most cases of listeriosis are caused by eating food contaminated with listeria. Listeria is most commonly found in unpasteurised milk and dairy products made from unpasteurised milk.

Listeria can also be found in food manufacturing environments and can contaminate food products after production. For example, contamination can occur:

after the food is cooked, but before it's packaged
when food is handled in shops, such as on slicing machines or delicatessen counters
in the home

Vegetables can be contaminated if they're grown in contaminated soil or fertiliser, or if they're washed in contaminated water. Meat and dairy products can become contaminated if they're taken from infected animals.

Unlike most other types of bacteria, listeria can survive and often multiply in temperatures below 5C (41F). Therefore, listeria can still grow to potentially harmful levels in food stored in a fridge.

Read about preventing listeriosis.

Infected stools

It's thought that listeria can be found in the digestive systems of many animals, such as sheep and cattle, and these animals may pass stools contaminated with listeria.

It's estimated that up to 1 in 20 people may be carriers of listeria, but have no symptoms of listeriosis. Human carriers can also pass stools contaminated with listeria, which can spread if, for example, the carrier doesn't wash their hands after going to the toilet, then handles food.

At-risk groups

Some people are at an increased risk of developing listeriosis, including:

those over 65 years of age
pregnant women and their unborn babies
babies less than one month old
people with a weakened immune system, such as those with HIV or receiving chemotherapy

Pregnant women should avoid close contact with farm animals that are giving birth or have recently given birth. Read more about the potential risks of close contact with farm animals on GOV.UK.

Treatments

Most listeria infections don't need treatment, as the symptoms usually pass within three days.

Over-the-counter painkillers, such as paracetamol and ibuprofen, can offer some relief for muscle pain and fever, if you need it.

Diarrhoea and vomiting advice

If you have diarrhoea, it's important to drink plenty of fluids to replace those that have been lost. There are also a number of medications available, but these are rarely necessary. Read more about the treatment of diarrhoea.

If you've been vomiting or feeling sick, it should be fine to avoid eating for a short while. However, make sure you continue drinking fluids, and eat as soon as you can. Eat small, light meals and avoid fatty or spicy foods.

Contact your GP if your symptoms don't improve within a few days.

Severe listeriosis

If listeriosis spreads into the blood (septicaemia) or the central nervous system, you'll be admitted to hospital to receive injections of antibiotics (intravenous antibiotics) while your health is carefully monitored.

The length of time you'll need to spend in hospital depends on whether the infection has spread from your blood or nervous system to other organs, such as your brain.

Most people with severe listeriosis require at least two weeks of treatment with intravenous antibiotics. However, in the most serious cases, at least six weeks of treatment may be needed.

Listeriosis in infants

Treatment for listeriosis in infants is the same as for adults, although it's usually recommended that infants are kept in an intensive care unit (ICU) as a precaution.

Listeriosis in pregnancy

If you develop listeriosis during pregnancy, you'll be given antibiotics to help prevent the infection spreading to your baby. You may also be given additional ultrasound scans to assess the health of your baby.

Prevention

The best way to prevent getting listeriosis is to always ensure that you follow good basic food hygiene.

This includes:

Peeling raw vegetables, salads or fruit, or washing them thoroughly before eating.
Washing your hands before preparing food, before eating and after going to the toilet.
Washing kitchen surfaces and utensils regularly, particularly after preparing raw meat, poultry and eggs.
Always separating raw foods from ready-to-eat foods. Don't store raw meat above ready-to-eat foods, because there's a risk that juice containing harmful bacteria may leak from the raw meat.
Always cooking food thoroughly and checking cooking instructions carefully, including the cooking time.

For foods that are "ready to eat", the most important ways of reducing the risk of listeriosis are to:

not use food after its "use by" date
make sure that the temperature of your fridge is 0-5C
follow storage instructions on food labels

Read more information about food safety.

Advice for ‘at risk’ groups

People who are particularly vulnerable to a serious listeriosis infection include:

those over 65 years of age
pregnant women and their unborn babies
babies less than one month old
people with a weakened immune system – such as with HIV or those on medication, such as chemotherapy

If you're in a high-risk group for catching listeriosis, you should avoid eating foods known to be at risk of listeria contamination.

Foods to avoid include:

soft mould-ripened cheese – such as Brie, Camembert and chèvre (a type of goat's cheese)
soft blue-veined cheese – such as Danish blue and gorgonzola
all types of pâté – including vegetable pâté
unpasteurised milk
undercooked food

It's safe to eat hard blue-veined cheese during pregnancy, such as Stilton, as well as other types of hard cheese, including Cheddar and Parmesan – even if these are made from unpasteurised milk.

Read more about foods to avoid during pregnancy.

Farm animals

Pregnant women should avoid close contact with farm animals that are giving birth or have recently given birth. This is to avoid the small, but serious, risk of an infection.