Listeriosis

12 min read

What is listeriosis?

Listeriosis is an infection that usually develops after eating food contaminated by bacteria called Listeria monocytogenes, commonly known as listeria.

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, a severe headache and
tremors
.

Pregnant women are at an increased risk of developing listeriosis.

Read more about the

symptoms of listeriosis
.

Where is listeria found?

The listeria bacteria have been found in a range of chilled ‘ready-to-eat’ foods, including:

  • pre-packed sandwichesor salads
  • some pre-prepared fruit, including melon slices
  • pâté
  • butter
  • soft cheeses, such as Brie or Camembert or others with a similar rind
  • soft blue cheese
  • unpasteurised milk or products made from unpasteurised milk
  • cooked sliced meats, cold cuts and cured meats
  • smoked fish, such as salmon or trout, or cooked shellfish
  • undercooked food

Read more about

what causes listeriosis
.

Seeking medical help

If you are pregnant and show signs of listeriosis, or if you have a young child who shows signs of the illness, you should seek immediate medical advice. If you have a condition that weakens your immune system (such as cancer) or are taking medication that reduces it (such as steroids) and think you have listeriosis you should also seek immediate medical advice.

If you are not pregnant and are an otherwise healthy adult, should call 999 or go to A&E if your symptoms are severe.

Severe symptoms include:

  • a severe headache and stiff neck
  • find it uncomfortable to look at bright lights
  • having a fit or a seizure
  • feeling confused
  • feeling very sleepy or difficult to wake
  • a rash that does not fade when a glass is rolled over it
  • bleeding or bruising easily
  • a lack of physical coordination or balance
  • uncontrollable shaking or twitching (tremor)
  • feeling any of the following symptoms together
    • confusion
    • abdominal pain
    • shortness of breath
    • a high heart rate
    • fever, shivering
    • feeling very cold
    • extreme pain
    • sweaty skin

Listeriosis is usually diagnosed with a

blood test
. If it is thought that the infection has spread to the nervous system, further tests may include a
MRI scan
and a
lumbar puncture
.

Mild cases of listeriosis usually do not need treatment. However, if you are at risk of getting seriously unwell (for example, if you are pregnant) then you may need antibiotics. If the infection has spread to the nervous system, you'll need to be treated with antibiotics in hospital for several weeks.

Read more about the

treating listeriosis
.

Preventing listeriosis

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

  • wash your hands regularly
  • not use food that's past its ‘use by’ date
  • follow storage instructions on food labels and eat opened food within 2 days (unless the packet states differently)
  • make sure that the temperature of your fridge is between 0ºC and 5ºC
  • cook food thoroughly (including reheating food)
  • keep raw and ready-to-eat apart from one another
  • eat ready-to-eat foods within 4 hours of them being outside the fridge
  • wash fruit and vegetables before you eat them

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

Read more about

preventing listeriosis
.

'At-risk' groups

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

  • people over 60 years of age
  • pregnant women and their unborn babies
  • newborn babies
  • people with uncontrolled diabetes
  • people with a weakened immune system, such as those with
    HIV/AIDS
    or those receiving some types of medication such as
    chemotherapy

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.

Listeriosis it can cause pregnancy and birth complications, and can result in

miscarriage
or stillbirth. An estimated 22% of pregnancy-related cases of listeriosis will result in the death of the baby.

Listeriosis symptoms

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

They are similar to

flu
and
gastroenteritis
, including:

  • a high temperature (fever) of 38ºC (100.4ºF) or above
  • muscle ache or pain
  • chills
  • feeling sick
  • being sick
  • diarrhoea

These symptoms will 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 much more severe. You may also develop any combination of confusion, abdominal pain, shortness of breath, a high heart rate, fever, shivering, feeling very cold, extreme pain, or sweaty skin.

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

  • a severe headache and stiff neck
  • finding it uncomfortable to look at bright lights
  • having a fit or a seizure
  • feeling confused
  • feel very sleepy or difficult to wake
  • have a rash that does not fade when a glass is rolled over it
  • lack of physical co-ordination or balance
  • uncontrollable shaking or twitching (
    tremor
    )

If listeriosis spreads to the brain, it can cause

meningitis
. This is an infection of the membranes that surround the brain and spinal cord.

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 37ºC (98.6ºF). For more information, see [what is a high temperature in children?]

When to seek medical help

You should seek immediate medical help if:

  • you show any signs of severe listeriosis or are bleeding or bruising easily. Call 999 or go to A&E immediately
  • your child shows signs of listeriosis
  • you are pregnant with a fever and chills or you think you might have listeriosis
  • you have a weakened immune system or take medication that weakens your immune system and think you have listeriosis

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

Causes of listeriosis

Listeriosis is caused by a type of bacteria called Listeria monocytogenes (listeria). It is mainly spread through contaminated food.

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

It's thought that listeria may be present in the digestive systems of many animals, such as sheep and cattle, and that these animals 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.

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 is 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 animals infected with listeria.

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

Listeria cannot multiply in temperatures below the freezing point of 0ºC (32ºF), but freezing food doesn't necessarily kill all of the listeria bacteria.

Listeria can be removed by cooking food thoroughly or, in the case of dairy products, pasteurising it (a heat treatment designed to kill bacteria). You should also wash raw fruit and vegetables thoroughly before eating them.

For foods that are ready to eat, make sure your fridge is at the right temperature (between 0ºC and 5ºC), follow storage instructions on food labels and don't use food that's past its ‘use by’ date.

Read more about

preventing listeriosis
.

Treating listeriosis

Most listeria infections don't need specific 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 very important that you drink plenty of fluids to replace those that have been lost. There are also several 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 that you continue drinking fluids, and eat as soon as you can. Eat small, light meals and avoid fatty or spicy foods.

Make an urgent appointment for the diarrhoea and vomiting if:

  • your symptoms have not improved after a few days
  • you are dehydrated (having dark yellow and strong-smelling pee, are dizzy or have a dry mouth)

Go to the hospital emergency department immediately if you have:

  • your child might have listeriosis
  • you have blood in your poo or vomit
  • you are vomiting and cannot keep any fluids down
  • very bad abdominal pain, or your abdomen hurts when you press it
  • a swollen abdomen
  • a high fever
  • you haven’t peed all day
  • you feel faint, dizzy or confused
  • you have a fast heart rate or are breathing quickly
  • you feel weak and cannot do your normal activities

Severe listeriosis

If listeriosis spreads into the blood (

septicaemia
) or the central nervous system, you'll be admitted to hospital so that you can be given injections of
antibiotics
(intravenous antibiotics) while your health is carefully monitored.

The length of time that you'll need to spend in hospital will depend 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 that 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.

Preventing listeriosis

The best way to prevent getting listeriosis is to always ensure 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 (including reheating) and checking cooking instructions carefully, including the cooking time.
  • don't use food that's past its ‘use by’ date
  • follow storage instructions on food labels and eat opened food within 2 days (unless the packet states differently)
  • make sure that the temperature of your fridge is between 0ºC and 5ºC
    eat ready-to-eat foods within 4 hours of them being outside the fridge

Advice for ‘at risk’ groups

If you are in a high-risk group for catching listeriosis - for example, if you are pregnant or you have a weakened immune system, you should avoid eating foods that are known to be at risk of listeria contamination.

Different countries have differing recommendations so always discuss what foods you can and cannot eat with your doctor or midwife.

Foods which may have listeria include:

  • pre-packed sandwiches or salads
  • some pre-prepared fruit, including melon slices
  • all types of pâté, including vegetable pâté
  • butter
  • soft cheeses such as:
    • 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
  • unpasteurised milk or products made from unpasteurised milk
  • cooked sliced meats, cold cuts and cured meats
  • smoked fish, such as salmon and trout, or cooked shellfish
  • any undercooked food

It is safe to eat hard blue-veined cheese during pregnancy, such as Stilton, as well as other types of hard cheese, including Cheddar and Parmesan.

There are other foods that pregnant women should avoid during pregnancy,

here
.

Avoid close contact with farm animals that are giving birth or have recently giving birth if you are pregnant.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.