Food Poisoning Listeria

Overview

Listeria food poisoning, also called listeriosis, is an illness caused by eating food contaminated with a germ (bacteria) called Listeria monocytogenes. In most healthy people it causes a mild illness a bit like flu or a stomach bug, with fever, aches and sometimes diarrhoea. The reason doctors take it seriously is that this germ can, in some people, spread beyond the gut and cause a more serious infection of the blood or the lining of the brain. The people most at risk are pregnant women, newborn babies, adults over 65 and anyone with a weakened immune system. Unlike many food bugs, Listeria can keep growing slowly even in a cold fridge, which is why chilled, ready-to-eat foods are often the source.

Listeria food poisoning is much less common than food poisoning from germs like Campylobacter or Salmonella. In the UK and many other countries only a few hundred cases are confirmed each year, and most people who are exposed never become seriously ill. Because it is uncommon, it can be missed at first, which is one reason doctors ask about what you have eaten and whether you are pregnant.

Anyone can get it, but it causes serious illness mainly in four groups: pregnant women and their unborn babies, newborn babies, adults aged 65 and over, and people whose immune system is weakened by illness or by medicines that suppress it. Healthy children and healthy adults usually have mild symptoms or none at all.

Symptoms

Common symptoms

• Fever and chills
• Muscle aches and general flu-like feelings
• Headache
• Feeling sick or being sick
• Diarrhoea, sometimes with stomach cramps
• Tiredness and low energy

Symptoms in children

• Often mild or no symptoms at all in healthy children
• In newborn babies, listeria can cause poor feeding, being unusually sleepy or floppy, irritability, fever, vomiting or difficulty breathing
• A newborn with any of these signs needs urgent medical attention, because infection can be passed from mother to baby around birth

Symptoms in older adults

• Symptoms may be more severe and come on faster
• Confusion, dizziness or trouble with balance can be a warning sign of a more serious infection
• Severe headache, neck stiffness or sensitivity to light
• Feeling very weak, drowsy or less responsive than usual
• Dehydration from vomiting or diarrhoea can build up quickly and cause extra problems

Causes

Main causes

• Eating food containing the Listeria bacteria, which can grow in chilled, ready-to-eat foods
• Unpasteurised milk and cheeses made from raw milk
• Soft mould-ripened cheeses such as brie, camembert and blue-veined cheeses, and some soft cheeses made from unpasteurised milk
• Pâté and unpasteurised meat spreads
• Smoked or cured fish such as smoked salmon that has not been cooked
• Pre-packed sandwiches, sliced meats and other chilled foods that have been kept too long or stored above the recommended fridge temperature
• Raw or unwashed fruit and vegetables, and undercooked meat or poultry
• Cross-contamination in the kitchen, for example using the same board for raw meat and ready-to-eat food

Risk factors

• Being pregnant, because pregnancy changes the immune system and the infection can also affect the baby
• Being aged 65 or over
• Having a weakened immune system, for example from cancer treatment, an organ transplant, HIV, liver disease or long-term steroid medicines
• Taking medicines that reduce stomach acid, which can make it easier for bacteria to survive
• Being a newborn baby, especially if the mother had listeria around the time of birth
• Having diabetes or long-term kidney or liver conditions

When to see a doctor

See a doctor urgently if:

• You are pregnant and you have a fever, aches, or feel unwell after eating a higher-risk food
• You have a fever with a severe headache, neck stiffness, or you feel confused
• Your baby or young child has a fever, is feeding poorly, or is unusually sleepy or floppy
• You are over 65 or have a weakened immune system and develop fever or vomiting
• You cannot keep fluids down, or you feel very thirsty with little or no urine
• You have severe abdominal pain or blood in your stools

Book a routine appointment if:

• Mild fever, aches or diarrhoea that are not settling after a couple of days
• You would like advice on what to eat and drink while you recover
• You are unsure whether a food you ate was higher risk during pregnancy
• Symptoms keep coming back or you are worried about a pattern of food-related illness
• Someone in your household has similar symptoms and you want to know how to stop it spreading

Diagnosis

A doctor will usually start by asking about your symptoms, what you have eaten recently, any travel, and whether you are pregnant or have a condition that weakens your immune system. In a mild case, no tests may be needed. If you are in a higher-risk group, if symptoms are severe, or if the doctor suspects the infection has spread beyond the gut, they will take a sample to confirm it. Diagnosis is made by growing the bacteria from a sample or by detecting its genetic material.

Tests that may be done

• A blood test to look for the bacteria, which is the usual test when the doctor is concerned the infection has spread
• A stool (poo) sample, mainly when diarrhoea is the main symptom
• A sample of fluid from around the spine (lumbar puncture) if there are signs of infection in the brain or its lining; this is done in hospital
• Routine blood tests to check how your body is coping, such as salts, kidney function and infection markers
• Samples from the placenta or from the baby after birth, if a pregnant woman is affected

What to expect at your appointment

Results from a blood culture usually take one to three days, and longer for some tests. You may be offered treatment before results come back if your doctor is concerned. If you are sent home while waiting for results, you will be told what to do if symptoms get worse. If you are pregnant, you may be offered extra monitoring of your baby.

Treatment

For most healthy adults and children, treatment is rest and plenty of fluids, and the illness settles by itself. People in higher-risk groups, anyone with signs of a more serious infection, and most pregnant women are offered antibiotics, usually started quickly. Some people need to be looked after in hospital so fluids and antibiotics can be given into a vein and they can be monitored closely.

Self-care at home

• Drink small, frequent sips of water or an oral rehydration solution to replace fluids and salts
• Eat light, bland food when you feel ready, and do not force yourself to eat
• Rest as much as your body asks for
• Take paracetamol or ibuprofen only if it is suitable for you; ask a pharmacist or your doctor if you are unsure, pregnant, or taking other medicines
• Stay away from work, school or nursery until you have been free of diarrhoea and vomiting for at least 48 hours, and avoid preparing food for other people
• Wash hands thoroughly with soap and water after the toilet and before handling food
• Avoid close contact with anyone who is pregnant or has a weakened immune system while you are unwell

Medical treatments

When treatment is needed, doctors prescribe antibiotics. These are usually given by mouth for mild cases and into a vein (a drip) in hospital for anyone who is very unwell, pregnant, or has signs that the infection has spread. Pregnant women are usually offered antibiotics to protect both mother and baby, and a woman who feels unwell in late pregnancy may be advised to give birth in a hospital where the baby can be checked and treated if necessary. Your medical team will decide which treatment is right for you based on your symptoms, your test results and your general health.

When is surgery considered?

Surgery is not usually needed for listeria infection. Rarely, the bacteria can cause an abscess or infection in a joint, heart valve or other part of the body, which might need a procedure to drain or repair.

Living with this condition

While you are recovering, focus on rest, fluids and gentle food. Tiredness can linger for a week or two after the fever settles. Keep up simple handwashing and kitchen hygiene so others at home are not put at risk. If you are pregnant and have been treated, you will usually be offered follow-up checks, and you should go straight back if you notice any change in your baby's movements.

Lifestyle tips

• Keep your fridge at or below 5C and use a fridge thermometer so you can check
• Eat or freeze chilled ready-to-eat foods by their use-by date and never after it
• Wash hands after handling raw meat, and use separate boards and knives for raw and ready-to-eat food
• Reheat leftovers until they are steaming hot all the way through
• Wash fruit and vegetables thoroughly, or peel them, before eating them raw
• Avoid unpasteurised dairy products, pâté and unpasteurised soft cheeses if you are pregnant or have low immunity

Diet and exercise

During the illness, choose simple foods that appeal to you, such as toast, rice, soup or bananas, and drink often. There is no special diet that clears the infection. Once your appetite and energy come back, return to your normal balanced eating. Gentle activity such as short walks is fine when you feel up to it, but give yourself time before going back to harder exercise, and drink more than usual if you are active.

Mental health and emotional wellbeing

Being unwell, and especially being unwell in pregnancy, can bring worry, guilt about what you ate, and difficulty sleeping. These feelings are very common and they are not a sign of weakness. Tell your doctor, midwife or nurse how you are feeling; they can explain what is known, arrange follow-up and, if the worry is lasting, point you to talking support. If you ever feel you cannot cope, contact your local emergency number or a crisis support service right away.

Prevention

Yes, the risk can be greatly lowered, although it cannot be removed completely. Listeria is killed by thorough cooking, so eating food that has been properly heated is the single most effective protection. Careful fridge temperature, using up chilled foods in time, and good hand and kitchen hygiene also make a big difference. If you are pregnant or have a weakened immune system, avoiding a short list of higher-risk foods is sensible, and the advice is intended to be practical, not to make mealtimes frightening.

Vaccines

There is no vaccine for listeria. Protection comes from choosing and storing food safely and from seeking care early if you are in a higher-risk group.

Screening programmes

There is no routine screening test for listeria in people without symptoms, and screening is not needed after eating a food that was later recalled unless you become unwell. If you are pregnant and develop fever or feel unwell, you will be offered tests and treatment rather than screening. Public health teams do monitor food and reported cases, which is how outbreaks are spotted and foods withdrawn.

Complications

If left untreated

• In pregnant women, infection can lead to miscarriage, stillbirth, premature birth, or a very sick newborn baby
• The bacteria can spread to the blood (septicaemia), causing high fever, fast heartbeat and a drop in blood pressure
• Infection of the brain and its lining (meningitis) can cause severe headache, stiff neck, confusion and seizures
• Older adults and people with low immunity are more likely to need intensive hospital care
• Rarely, infection can affect the heart valves, joints, eyes or other organs
• Dehydration from vomiting and diarrhoea can be serious, particularly in babies and older people

Long-term outlook

For most healthy people the outlook is very good, with full recovery within about a week. For higher-risk groups, starting treatment early makes a real difference, and many people recover fully with appropriate care. If you are pregnant, your team will watch you and your baby closely, and there is a great deal they can do to help. It is natural to feel shaken by a serious infection, but prompt medical care, follow-up and the support of your family and health team all improve the chances of a good outcome.

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