Everything you need to know about Norovirus

Globally, about 685 million cases of norovirus are reported each year. Of that estimate, over 200 million cases affect children.

In February 2023, government data showed that laboratory reports of the virus were 66% higher than the average for that time of year. Outbreaks can happen at any time, but they occur most often from November to April. According to the Food Standards Agency, it causes an estimated three million cases of diarrhoea and vomiting each year, and 380,000 cases are linked to food. In care homes, it is the most common cause of gastrointestinal infection.

Norovirus is highly contagious and is easily spread through contact with someone who has the infection or with contaminated surfaces or food.

What is norovirus?

Norovirus is a type of stomach bug which causes symptoms of vomiting and diarrhoea. It is also known as the winter vomiting bug. The symptoms are usually quite severe and can be very unpleasant but you will usually feel better within a couple of days, without any long-term health issues.

It is caused by a virus which is highly contagious, which means it can spread quickly between people. This means that outbreaks are common, particularly in the winter months.

There are many different strains of norovirus, which means it is possible that you can become unwell with norovirus multiple times throughout your lifetime, as infection with one type of norovirus may not protect you against other types.

What causes norovirus?

A virus in the Caliciviridae family causes norovirus. When the virus enters your body it makes your stomach and intestines swell or become inflamed, a condition called gastroenteritis.

There are several different strains of norovirus. The Caliciviridae family of viruses are responsible for causing the inflammation of your stomach and intestines. In this family of viruses, there are 10 groups with 48 different types. If you have the virus, your body releases billions of tiny virus particles that can spread to other people and make them unwell.

Symptoms of norovirus

The symptoms of norovirus usually begin quite suddenly, and within 1-2 days after becoming infected.

The main symptoms of norovirus are:

• Nausea
• Sickness
• Diarrhoea
• Stomach cramps

Some people also experience:

• A high temperature
• An aching body
• A headache
• Feeling generally unwell

Some people with norovirus infection may show no signs or symptoms. However, they will still be contagious and can still spread the virus to other people.

If you are vomiting and have diarrhoea, this is usually caused by norovirus or another stomach bug.

Other potential causes are:

• Food poisoning
• Food intolerance or allergy
• Irritable bowel syndrome
• Inflammatory bowel disease
• Coeliac disease.

Food poisoning is an umbrella term that refers to different types of food and water-borne bacteria, viruses and parasites. Food poisoning and stomach bugs are essentially the same things. Both are a result of a viral or bacterial infection which results in inflammation in the lining of the gut, known as gastroenteritis. This is what causes the usual symptoms of vomiting, nausea, diarrhoea and loss of appetite.

For further reading about the different viruses and bacteria that can cause food poisoning, please see our knowledge base.

How is norovirus spread?

Norovirus is highly contagious, meaning it can spread easily between people. If you have viral gastroenteritis such as norovirus, it will be present in your stool and vomit. You may spread the virus in small bits of stool or vomit, especially if you don’t wash your hands thoroughly after using the toilet.

Norovirus is most commonly spread through:

• Eating food which has been contaminated during preparation.
• Touching contaminated surfaces and then putting your hands in your mouth.
• Being in close contact with a person who has norovirus.

Foods which are at increased risk of being contaminated include:

• Shellfish
• Leafy vegetables
• Salad
• Fruit
• Ready-to-eat foods

Norovirus does not multiply in food, but it can survive on it for long periods of time.

When an infected person vomits, the virus may become airborne and land on surfaces, or on another person.

If water comes into contact with the stools of infected people, the water may become contaminated with a virus. The contaminated water can spread the virus to foods or drinks, and people who consume these foods or drinks may become infected. People who swim in contaminated water may also become infected.

Norovirus can remain on objects and surfaces and continue to infect people for days and even weeks. Norovirus can survive some disinfectants, making it difficult to get rid of.

Infected people who do not have symptoms can still spread viruses. Norovirus may be found in your stool before you have symptoms and up to two weeks after you recover.

Who is at risk of norovirus?

Norovirus most often occurs in environments where people are in close contact. This can include closed and crowded environments.

Examples of settings where norovirus can spread easily include:

• Hospitals
• Care homes
• Schools
• Childcare settings
• Cruise ships
• Hotels or resorts where people are in close proximity

It is particularly important for people who work in these environments to be extra cautious and practise good hygiene, particularly in settings where people may be more vulnerable, for example in care homes or hospitals.

For further reading about food safety and hygiene in care homes, please see our knowledge base.

Although the symptoms of norovirus can be very unpleasant, people usually recover quickly, within 1-3 days. It can sometimes persist for longer in certain individuals, for example young children, elderly people or people with weakened immune systems.

How long is the infection contagious?

People with norovirus are contagious from when they first begin feeling unwell, until at least two days after their symptoms have stopped. You should avoid contact with other people while you have symptoms and for two days after the last time you vomited or had diarrhoea. This is when the infection is most contagious.

Some people may be contagious for as long as two weeks after recovery. It is therefore particularly important for people to use good handwashing and take other preventative measures, even after recovering from the norovirus illness.

How is norovirus prevented?

Norovirus is highly contagious; however, there are some preventative steps you can take.

These include:

• Washing your hands for at least 20 seconds with soap and warm water. This is especially important after you have been to the toilet, changed a nappy, before you prepare food or before you eat or drink anything.
• Try to avoid contaminated food or water. This includes food that was prepared by someone who may be unwell.
• Ensure seafood is cooked thoroughly.
• Wash fruit and vegetables thoroughly before using them.
• Be extra cautious when travelling. This may include only eating cooked foods and drinking hot beverages and avoiding eating from street vendors. This is particularly important when travelling to a place where there is a high risk of norovirus infection. For tips on how to avoid food poisoning on holiday, please see our knowledge base.
• Disinfect surfaces which may have been contaminated with norovirus. Use a chlorine bleach solution or a disinfectant that is effective against noroviruses.

You can help prevent the spread to other people by:

• Staying at home while you are unwell and for two days after your symptoms have stopped; this includes keeping your child away from school or nursery, staying off work and avoiding travel during this time.
• Do not visit hospitals or care homes during this time.
• Do not prepare food for other people while you are unwell with norovirus and for two days after your symptoms have stopped.
• Wash any clothes or bedding separately on a hot wash, especially if they have been soiled.
• Clean toilet seats, flush handles, taps, surfaces and door handles regularly and thoroughly.
• Do not share towels, flannels, cutlery or utensils.
• Do not use a shared swimming pool for two weeks after your symptoms stop.

Alcohol-based hand sanitisers are not as effective against norovirus as washing your hands with soap and warm water.

It is vital that any setting that handles food ensures that all staff members have up-to-date food hygiene training and understand the risks. Food hygiene training is important as it ensures that both staff and customers are kept safe.

How is norovirus treated?

There isn’t a cure for norovirus. Treatment for the infection focuses on relieving your symptoms. If you, your child or someone you are caring for has norovirus, it can usually be treated at home. The most important thing is to avoid becoming dehydrated by drinking plenty of fluids. Norovirus can make it difficult for you to eat or drink because the inflammation in your intestines and stomach causes you to vomit or have diarrhoea.

While you are unwell with norovirus you should:

• Keep hydrated with water. Frequent, small sips are enough if this is all you can manage.
• Stay at home and get plenty of rest.
• When you feel able to eat something, eat a little bit initially. You do not need to avoid any certain foods, just eat whatever you can manage.
• Take paracetamol if you are uncomfortable or in any pain.
• Continue to breastfeed or formula feed your baby. If they are being sick, offer smaller, more regular feeds.
• If your baby is formula fed or on solid food, you can also offer small sips of water in addition.

You should not:

• Drink fruit juice or fizzy drinks as this can make symptoms of diarrhoea worse.
• Give children under 12 years old any medicine to stop diarrhoea.
• Give aspirin to children under 16.
• Water down baby formula as this can be dangerous.

Speak to your pharmacist if you need any advice while you have diarrhoea and vomiting.

They may recommend:

• Oral rehydration sachets that you mix with water to make a drink. This helps to rebalance the body and helps you to recover and feel better more quickly.
• Medicine that can stop diarrhoea for a few hours; these types of medicine are not suitable for children under 12 years old.

You should get advice from a medical professional or call 111 if:

• A baby refuses breast or bottle feeds while they are unwell.
• You are worried about a baby under 12 months old.
• A child under 5 years old is showing any signs of dehydration.
• Either you or your child who is over 5 years old are showing signs of being dehydrated, even after using rehydration sachets.
• You or your child cannot keep any fluid down.
• You or your child are bleeding from your bottom or have blood in your diarrhoea.
• You or your child are still being sick after 2 days or still have diarrhoea after 7 days.

You should call 999 or go to your nearest A&E if:

• You have yellow or green vomit.
• You have blood in your vomit or your vomit looks like ground coffee.
• Have a sudden, severe headache or stomach ache.
• You think you or your child might have swallowed something poisonous.
• Have a stiff neck or pain when looking at bright lights.

For most people, norovirus clears up in 1-3 days with no long-term symptoms and it is not life-threatening. However, it can be more serious for some people, especially those with weakened immune systems, other underlying health conditions, the elderly, very young children and pregnant women. Norovirus has the potential to cause severe dehydration which can be serious.

Dehydration occurs when your body doesn’t have enough water to carry out its normal functions. This may be because you are losing more water than you are taking in.

Symptoms of dehydration include:

• Headaches
• Dizziness or light-headedness
• Feeling tired
• Dry mouth and throat
• Dark coloured, strong smelling urine
• Dry skin
• Muscle cramps
• Sunken eyes

Symptoms of dehydration in a baby may include:

• A sunken soft spot (fontanelle) on top of their head
• Sunken eyes
• Few wet nappies
• Little or no tears when they cry
• Being drowsy or irritable

Anyone with signs or symptoms of dehydration should see a doctor straight away. A person with severe dehydration may need treatment in hospital.

The NHS offer a useful factsheet about dehydration, including the causes and what to do if you think you or your child may be dehydrated.