Listeriosis

Overview

Listeriosis is an infection caused by a type of bacteria called Listeria. Most people get it by eating food that contains the bacteria. For many healthy people it causes only a mild illness, or no symptoms at all. But for some groups — especially pregnant people, newborn babies, older adults and people whose immune system is weakened — it can be much more serious. 'Immune system' means the body's natural defence against infection. Listeriosis can be treated, and most people recover well, especially when it is found early.

Listeriosis is uncommon. Many people are exposed to Listeria at some point without ever becoming unwell or being diagnosed. Serious cases are rare, but they are the reason food safety advice exists.

Anyone can get listeriosis, but it is most dangerous for pregnant people and their unborn babies, newborn babies, adults over 65, and people with weakened immune systems — for example those having certain cancer treatments, organ transplant medicines, or living with conditions such as HIV. Healthy children and adults usually have mild illness or none.

Symptoms

Common symptoms

• Fever
• Muscle aches or feeling generally fluey
• Feeling sick (nausea) or being sick
• Diarrhoea
• Headache
• Tiredness

Symptoms in children

• Usually mild or no symptoms in healthy children
• Fever and irritability
• Vomiting or diarrhoea
• Poor feeding in babies
• Newborns may be sleepy, floppy, feed poorly, or have breathing problems — this needs urgent medical attention

Symptoms in older adults

• Fever and muscle aches
• Confusion or a change in usual alertness
• Headache with a stiff neck
• Feeling unsteady or having trouble with balance
• Tiredness and loss of appetite that gets worse over days

Causes

Main causes

• Eating food containing Listeria bacteria — for example unpasteurised (raw) milk and dairy products, soft cheeses like mould-ripened or blue-veined types, pâté, chilled ready-to-eat meats such as sliced deli meats and hot dogs, smoked or cured fish, and pre-prepared cold foods like sandwiches and salads
• Eating raw or lightly cooked food that has not been heated through, such as undercooked meat or raw sprouts
• Unwashed raw fruit and vegetables, or produce cut and stored for a long time
• Cross-contamination in the kitchen — for example using the same board or knife for raw food and ready-to-eat food
• A fridge that is not cold enough, allowing bacteria to multiply in stored food
• Rarely, passing the infection from a pregnant person to the baby, or from mother to newborn during birth

Risk factors

• Being pregnant
• Being over 65
• Having a weakened immune system, such as from certain medicines, chemotherapy, or long-term conditions
• Being a newborn baby
• Drinking raw (unpasteurised) milk or eating foods made from it
• Eating chilled ready-to-eat foods that are not reheated
• Living in a place with poor food refrigeration or food hygiene

When to see a doctor

See a doctor urgently if:

• You are pregnant and have a fever, aches, or feel unwell — even mild symptoms should be checked the same day
• You have a fever and a weakened immune system
• You are over 65 with a fever, headache, or feeling increasingly unwell
• You have a severe headache with a stiff neck
• You have diarrhoea or vomiting that lasts more than a couple of days, or signs of dehydration
• A newborn or young baby has a fever, is sleepy, floppy, or feeding poorly

Book a routine appointment if:

• You are unsure whether a food you ate was safe and you have no symptoms — you can ask a pharmacist or your doctor for advice
• You have mild, short-lived tummy upset and want to know what to watch for
• You want advice on safe foods to eat during pregnancy
• You have questions after an outbreak warning about a particular food product

Diagnosis

A doctor will ask about your symptoms, what you have eaten recently, your pregnancy or health history, and any medicines you take. Listeriosis is confirmed with laboratory tests, usually on a sample of blood. In pregnancy, tests may include samples related to the pregnancy. Because symptoms can be mild and vague, many mild cases are never formally diagnosed — the tests are mainly used when someone is unwell enough to need medical care.

Tests that may be done

• Blood test (blood culture) to look for the bacteria — the most common test
• Spinal fluid test (lumbar puncture) if there are signs of infection around the brain
• Placental, amniotic fluid, or vaginal swab tests in pregnancy when advised
• Occasionally stool (poo) testing during a food outbreak investigation
• Brain scans such as MRI if infection is thought to affect the brain

What to expect at your appointment

You may be asked to come to hospital for tests, especially if you are pregnant or in a higher-risk group. A blood test is quick and feels like a small pinch. A lumbar puncture is done with numbing medicine and is only used when it is clearly needed. Test results for Listeria can take a few days, so doctors may start treatment based on suspicion rather than wait. Ask your care team to explain each step — you are always allowed to ask questions.

Treatment

Most healthy people with mild listeriosis recover on their own within a few days with rest and fluids. People at higher risk — pregnant people, older adults, newborns, and those with weakened immunity — are offered antibiotic treatment, because the infection can spread to the blood, the brain, or the baby. Antibiotics are medicines that kill bacteria. Treatment is usually given through a drip in hospital and started early, without waiting for test results.

Self-care at home

• Drink plenty of fluids to replace what you lose through vomiting or diarrhoea
• Rest and eat light meals when you feel ready
• Use rehydration drinks if advised by a pharmacist — ask them about products suitable for you
• Wash your hands well after using the toilet, and clean surfaces you use
• Do not prepare food for others while you have symptoms
• Keep note of your symptoms so you can describe them clearly to a doctor

Medical treatments

For people at higher risk, doctors prescribe a course of antibiotics given in hospital, usually through a drip into a vein. Sometimes two different antibiotics are used together. Treatment may be given at home or in hospital after assessment, and it may continue for weeks depending on how serious the infection is. Newborn babies and people with infection around the brain or in the blood need close monitoring. Because Listeria is best treated early, doctors often start treatment before test results come back. Your team will explain what you are being given and why.

When is surgery considered?

Surgery is not usually part of treating listeriosis. It is only considered in rare cases — for example if an infection has caused a collection of pus or damage in a part of the body that needs draining or repair. Your doctor will discuss this fully if it ever applies to you.

Living with this condition

For a mild case, expect to feel off for a few days to a week — tired, achy, and possibly with an upset stomach. Take it gently and go back to normal activity as you feel able. If you are having antibiotic treatment, you may need to stay in hospital for a while, and you will have follow-up appointments afterwards. If you are pregnant and have been treated for listeriosis, your baby will be monitored, and there is good evidence that early treatment greatly improves outcomes.

Lifestyle tips

• Clean out your fridge regularly and keep it at or below 5°C (40°F)
• Cook meat, poultry, and eggs thoroughly until piping hot all the way through
• Reheat chilled ready-to-eat foods until steaming hot before eating
• Wash raw fruit and vegetables well, and separate raw and cooked food in the kitchen
• Wash hands with soap and water before and after preparing food
• Wash kitchen surfaces and utensils that have touched raw food

Diet and exercise

There is no special diet that treats listeriosis, but gentle, regular meals and plenty of fluids help you recover. While you have symptoms, plain foods may sit better. After you feel better, a balanced, varied diet with plenty of fruits and vegetables supports your general health. Rest while unwell, then slowly return to normal movement and exercise. If you are pregnant or have a weakened immune system, ask your care team for a simple list of foods to avoid — most involve unpasteurised dairy, soft mould-ripened cheeses, pâté, and chilled ready-to-eat meats or fish.

Mental health and emotional wellbeing

A Listeria diagnosis can feel frightening, especially during pregnancy or for families with a newborn. Anxiety, feeling on edge, and going back over every meal you ate are very common and understandable reactions. These feelings usually ease as symptoms improve and appointments go well. Talk to someone you trust, and tell your care team if worry is affecting your sleep, appetite, or daily life — support is available and asking for it is a sign of strength. If you are in crisis or having thoughts of harming yourself, contact your local crisis service or your local emergency number straight away.

Prevention

Yes, largely. Listeria is killed by thorough cooking and held back by good refrigeration and kitchen hygiene. People in higher-risk groups are advised to avoid certain foods, such as unpasteurised dairy products, soft mould-ripened and blue-veined cheeses, pâté, and chilled ready-to-eat meats, smoked fish, and pre-made cold sandwiches — or to reheat these until steaming hot. Follow any local food safety alerts about recalled products.

Vaccines

There is no vaccine for listeriosis. Protection comes from food safety and hygiene.

Screening programmes

There is no routine screening test for listeriosis in people without symptoms. During a food outbreak, public health teams may test or recall specific foods and may advise testing for people who are at higher risk and ate those products. If you are pregnant and worried about a specific product, ask your midwife or doctor for advice.

Complications

If left untreated

• Spread of infection into the blood (sepsis), which can make you very unwell
• Infection of the brain or the tissues around it, causing severe headache, confusion, or seizures
• In pregnancy: miscarriage, stillbirth, or severe infection in the newborn baby
• In newborns: infection of the blood or brain that needs urgent hospital treatment
• Longer recovery or lasting after-effects in people who were already very unwell or had weakened immunity

Long-term outlook

The outlook is good for most people. Healthy adults usually recover fully after a short illness, often without any treatment. When Listeria infection is caught early and treated with antibiotics, most people recover well, including pregnant people and their babies. Babies treated promptly generally do well, though they may need a period of monitoring in hospital. Serious complications are uncommon, and doctors and midwives know to act quickly when listeriosis is suspected — so early advice is genuinely worthwhile.

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