Noroviruses are a group of viruses that can cause gastroenteritis. Gastroenteritis is an infection of the gut (intestines) which usually causes symptoms such as being sick (vomiting) and diarrhoea. Norovirus is the most common virus causing gastroenteritis in adults in the UK. In most cases the infection clears within a few days but sometimes takes longer. The main risk is lack of fluid in the body (dehydration). The main treatment is to have plenty to drink; this may mean special rehydration drinks. Also, once any dehydration is treated with drinks, you should eat as normally as possible. See a doctor if you suspect that you are becoming dehydrated, or if you have any worrying symptoms which are listed below.
What is norovirus?
Noroviruses are a group of viruses that can cause infection of the gut (intestines), called gastroenteritis. Viruses are types of germs smaller than bacteria. Gastroenteritis usually causes symptoms of being sick (vomiting) and diarrhoea. Norovirus is the newer name given to the group of viruses that used to be known as Norwalk-like viruses and Norwalk virus. Noroviruses are also known as small round-structured viruses (SRSVs).
How is norovirus spread?
A norovirus present in the gut (intestines) of an infected person can pass out in their diarrhoea. It is easily spread from an infected person to another by close contact. This is usually because of the virus being present on the infected person's hands after they have been to the toilet. Surfaces or objects touched by the infected person can also allow transmission of the virus. The virus can be passed on if the infected person prepares food or if water is contaminated with norovirus.
Outbreaks of norovirus that affect many people can occur. For example, in hospitals, on cruise ships and in schools.
It usually takes 24-48 hours after first contact with norovirus before symptoms develop. This period is known as the incubation period for the virus.
How common is norovirus infection and who gets it?
Norovirus is the most common virus causing infection of the gut (gastroenteritis) in adults in the UK. However, norovirus infection can occur in anyone of any age. You can get norovirus infection more than once because your body is not able to maintain immunity to norovirus infection for a long time once you have had it.
What are the symptoms of norovirus infection?
Feeling sick (nausea) is usually the first symptom. This is followed by diarrhoea which tends to be watery. You may also start being sick (vomiting) around the same time. Sometimes there are other symptoms such as:
- A high temperature (fever).
- A headache.
- Aching muscles in your arms and legs.
The symptoms tend to be relatively mild and short-lived, often only lasting one to two days. However, in a few people symptoms can last longer.
If symptoms are severe, lack of fluid in the body (dehydration) can occur. You should consult a doctor quickly if you suspect that you or your child are becoming dehydrated. Mild dehydration is common and is usually easily reversed by drinking lots of fluids. Severe dehydration can be fatal unless quickly treated because the organs of your body need a certain amount of fluid to function.
Symptoms of dehydration in children
- Symptoms of dehydration in children include:
- Passing little urine.
- A dry mouth; a dry tongue and lips.
- Fewer tears when crying.
- Sunken eyes.
- Being irritable or lacking in energy (lethargic).
- Symptoms of severe dehydration in children include:
- Pale or mottled (blotchy) skin.
- Cold hands or feet.
- Very few wet nappies.
- Fast (but often shallow) breathing.
Severe dehydration is a medical emergency and immediate medical attention is needed.
Dehydration is more likely to occur in:
- Babies under the age of 1 year (and particularly those under 6 months old). This is because babies don't need to lose much fluid to lose a significant proportion of their total body fluid.
- Babies under the age of 1 year who were a low birth weight and who have not caught up with their weight.
- A breast-fed baby who has stopped breast-feeding during their illness.
- Any baby or child who does not drink much when they are unwell.
- Any baby or child with severe diarrhoea and vomiting (particularly if they have passed six or more diarrhoeal stools and/or vomited three or more times in the previous 24 hours).
Symptoms of dehydration in adults
- Symptoms of dehydration in adults include:
- Dizziness or light-headedness.
- Muscular cramps.
- Sunken eyes.
- Passing little urine.
- A dry mouth and tongue.
- Becoming irritable.
- Symptoms of severe dehydration in adults include:
- Rapid heart rate.
- A greatly reduced amount of urine.
Severe dehydration is a medical emergency.
Dehydration in adults is more likely to occur in:
- Elderly or frail people.
- Pregnant women.
- People with severe diarrhoea and vomiting. In particular, if they are not able to replace the fluid lost with sufficient drinks.
How is norovirus diagnosed?
A sample of your stool (faeces) may be sent to the laboratory for testing during an outbreak of infection of the gut (gastroenteritis). This is to help identify the type and source of the infection. However, in most cases testing is not necessary because the treatment is usually the same for many causes of gastroenteritis.
When should I seek medical advice?
Most children who have infection of the gut (gastroenteritis), including gastroenteritis caused by norovirus infection, have mild symptoms which will get better within a few days. The important thing is to ensure that your child has plenty to drink. In many cases, you do not need to seek medical advice. However, you should seek medical advice in the following cases (or if there are any other symptoms that you are concerned about):
- If your child is under the age of 6 months.
- If your child has an underlying medical condition (for example, heart or kidney problems, diabetes, history of premature birth).
- If your child has a high temperature (fever).
- If you suspect lack of fluid in the body (dehydration) is developing (see earlier).
- If your child appears drowsy or confused.
- If your child is being sick (vomiting) a lot and unable to keep fluids down.
- If there is blood in their diarrhoea or vomit.
- If your child has severe tummy (abdominal) pain.
- If your child has a weakened immune system because of, for example, chemotherapy treatment, long-term steroid treatment, HIV infection.
- Infections caught abroad.
- If your child has severe symptoms, or if you feel that their condition is getting worse.
- If your child's symptoms are not settling - for example, vomiting for more than 1-2 days, or diarrhoea that does not start to settle after 5-7 days.
Again, most adults who have gastroenteritis, including gastroenteritis caused by norovirus infection, have mild symptoms which will get better within a few days. The important thing is to ensure that you have plenty to drink. In many cases, you do not need to seek medical advice. However, you should seek medical advice in the following cases (or if there are any other symptoms that you are concerned about):
- If you suspect that you are becoming dehydrated.
- If you are vomiting a lot and unable to keep fluids down.
- If you have blood in your diarrhoea or vomit.
- If you have severe abdominal pain.
- If you have severe symptoms, or if you feel that your condition is getting worse.
- If you have a continuing high fever.
- If your symptoms are not settling - for example, vomiting for more than 1-2 days, or diarrhoea that does not start to settle after 3-4 days.
- Infections caught abroad.
- If you are elderly or have an underlying health problem such as diabetes, epilepsy, inflammatory bowel disease, kidney disease.
- If you have a weakened immune system because of, for example, chemotherapy treatment, long-term steroid treatment, HIV infection.
- If you are pregnant.
What is the treatment for norovirus in children?
There is no special medication to treat norovirus. The aim is to make sure that your child has plenty of fluids to avoid lack of fluid in the body (dehydration) until their immune system has the time to clear the infection. Children with norovirus can usually be cared for at home. Occasionally, admission to hospital is needed if symptoms are severe, or if complications develop.
The following are commonly advised until symptoms ease:
Fluids to prevent dehydration
You should encourage your child to drink plenty of fluids. The aim is to prevent dehydration. The fluid lost in their sick (vomit) and/or diarrhoea needs to be replaced. Your child should continue with their normal diet and usual drinks. In addition, they should also be encouraged to drink extra fluids. However, avoid fruit juices or fizzy drinks, as these can make diarrhoea worse.
Babies under 6 months old are at increased risk of dehydration. You should seek medical advice if they develop gastroenteritis. Breast-feeds or bottle-feeds should be encouraged as normal. You may find that your baby's demand for feeds increases. You may also be advised to give extra fluids (either water or rehydration drinks) in between feeds.
Rehydration drinks may be advised by a healthcare professional for children at increased risk of dehydration (see above for whom this may be). They are made from sachets available from pharmacies and on prescription. You should be given instructions about how much to give. Rehydration drinks provide a perfect balance of water, salts and sugar. The small amount of sugar and salt helps water to be absorbed better from the gut (intestines) into the body. Home-made salt/sugar mixtures are used in developing countries if rehydration drinks are not available but they have to be made carefully, as too much salt can be dangerous to a child. Rehydration drinks are cheap and readily available in the UK and are the best treatment for your child.
If your child vomits, wait 5-10 minutes and then start giving drinks again but more slowly (for example, a spoonful every 2-3 minutes). Use of a syringe can help in younger children who may not be able to take sips.
Note: if you suspect that your child is dehydrated, or is becoming dehydrated, you should seek medical advice urgently.
Fluids to treat dehydration
If your child is mildly dehydrated, this may be treated by giving them rehydration drinks. Read the instructions carefully for advice about how to make up the drinks and about how much to give. This can depend on the age and the weight of your child. If you are breast-feeding, you should continue with this during this time. It is important that your child is rehydrated before they have any solid food.
Sometimes a child may need to be admitted to hospital for treatment if they are dehydrated. Treatment in hospital usually involves giving rehydration solution via a special tube called a nasogastric tube. This tube passes through your child's nose, down their throat and directly into their stomach. An alternative treatment is with fluids given directly into a vein (intravenous fluids).
Eat as normally as possible once any dehydration has been treated
Correcting any dehydration is the first priority. However, if your child is not dehydrated (most cases), or once any dehydration has been corrected then encourage them to have their normal diet. Do not starve a child with infection of the gut (gastroenteritis). This used to be advised but is now known to be wrong. So:
- Breast-fed babies should continue to be breast-fed if they will take it. This will usually be in addition to extra rehydration drinks (described above).
- Bottle-fed babies should be fed with their normal full-strength feeds if they will take it. Again, this will usually be in addition to extra rehydration drinks (described above).
- Older children - offer them some food every now and then. However, if he or she does not want to eat, that is fine. Drinks are the most important and food can wait until their appetite returns.
Anti-secretory medicines (racecadotril) are designed to be used with rehydration treatment. They reduce the amount of water that is released into the gut during an episode of diarrhoea. They can be used for children who are older than 3 months of age (and for adults). However, you can give paracetamol or ibuprofen to ease a high temperature (fever) or headache. Antibiotic medicines are not needed to treat norovirus. It is a viral infection so antibiotics will not be effective.
What is the treatment for norovirus in adults?
Symptoms often settle within a few days or so as your immune system usually clears the infection. Occasionally, admission to hospital is needed if symptoms are severe, or if complications develop (see below). The following are commonly advised until symptoms ease.
Fluids - have lots to drink
The aim is to prevent lack of fluid in the body (dehydration), or to treat dehydration if it has developed.
Note: if you suspect that you are dehydrated, you should contact a doctor.
- As a rough guide, drink at least 200 mls after each bout of diarrhoea (after each watery stool).
- This extra fluid is in addition to what you would normally drink. For example, an adult will normally drink about two litres a day but more in hot countries. The above advice about 200 mls after each bout of diarrhoea is in addition to this usual amount that you would drink.
- If you have been sick (vomited), wait 5-10 minutes and then start drinking again but more slowly. For example, a sip every 2-3 minutes but making sure that your total intake is as described above.
- You will need to drink even more if you are dehydrated. A doctor will advise on how much to drink if you are dehydrated.
For most adults, fluids drunk to keep hydrated should mainly be water. It is best not to have drinks that contain a lot of sugar, such as cola or pop, as they can sometimes make diarrhoea worse.
Rehydration drinks are recommended in people who are frail, or over the age of 60, or who have underlying health problems. They are made from sachets that you can buy from pharmacies. (The sachets are also available on prescription.) You add the contents of the sachet to water. Rehydration drinks provide a good balance of water, salts and sugar. They do not stop or reduce diarrhoea. However, the small amount of sugar and salt helps the water to be absorbed better from the gut (intestines) into the body. As with children, do not use home-made salt/sugar drinks, as the quantity of salt and sugar has to be exact.
Eat as normally as possible
It used to be advised not to eat for a while if you had infection of the gut (gastroenteritis). However, now it is advised to eat small, light meals if you can. Be guided by your appetite. You may not feel like food and most adults can do without food for a few days. Eat as soon as you are able but don't stop drinking. If you do feel like eating, avoid fatty, spicy or heavy food. Plain foods such as wholemeal bread and rice are good foods to try eating.
Antidiarrhoeal medicines are not usually necessary. However, you may wish to reduce the number of trips that you need to make to the toilet. You can buy antidiarrhoeal medicines from pharmacies. The safest and most effective is loperamide. The adult dose of this is two capsules at first. This is followed by one capsule after each time you pass some diarrhoea, up to a maximum of eight capsules in 24 hours. Loperamide works by slowing down your gut's activity. You should not take loperamide for longer than five days.
Note: do not use antidiarrhoeal medicines if you pass blood or mucus with the diarrhoea or if you have a high temperature (fever). People with certain conditions should not take loperamide. Therefore, read the leaflet that comes with the medicine to be safe. For example, pregnant women and children should not take loperamide.
Anti-secretory medicines (racecadotril) can be taken with rehydration treatment. They reduce the amount of water that is released into the gut during an episode of diarrhoea.
Paracetamol or ibuprofen is useful to ease a high temperature or headache. Antibiotics are not effective against viral infections so antibiotics are not needed to treat norovirus.
Are there any complications?
Complications of norovirus infection are not very common. If they do occur, they can include the following:
- Lack of fluid (dehydration) and salt (electrolyte) imbalance in your body. This is the most common complication. It occurs if the water and salts that are lost in your stools (faeces), or when you have been sick (vomited), are not replaced by your drinking adequate fluids. If you can manage to drink plenty of fluids then dehydration is unlikely to occur, or is only likely to be mild and will soon recover as you drink. Severe dehydration can lead to a drop in your blood pressure. This can cause reduced blood flow to your vital organs. If dehydration is not treated, kidney failure may also develop.
- Lactose intolerance can sometimes occur for a period of time after norovirus infection. It is known as secondary or acquired lactose intolerance. Your intestinal (gut) lining can be damaged by the episode of infection of the gut (gastroenteritis). This leads to lack of an enzyme called lactase that is needed to help the body digest the milk sugar lactose. Lactose intolerance leads to bloating, tummy (abdominal) pain, wind and watery stools after drinking milk. The condition gets better when the infection is over and the intestinal lining heals.
- Irritable bowel syndrome is sometimes triggered by a bout of gastroenteritis.
- Persistent diarrhoeal syndromes may (rarely) develop.
- Reduced effectiveness of some medicines. During an episode of gastroenteritis, certain medicines that you may be taking for other conditions or reasons may not be as effective. This is because the diarrhoea and/or vomiting means that reduced amounts of the medicines are taken up (absorbed) into your body. Examples of such medicines are medicines for epilepsy, diabetes and contraception. Speak to your doctor or practice nurse if you are unsure of what to do if you are taking other medicines and have gastroenteritis.
Preventing spread of infection to others
If you or your child have norovirus infection, the following are recommended to prevent the spread of infection to others:
- Wash your hands thoroughly after going to the toilet. Ideally, use liquid soap in warm running water but any soap is better than none. Dry properly after washing. If your child wears nappies, be especially careful to wash your hands after changing nappies and before preparing, serving, or eating food.
- If a potty has to be used, wear gloves when you handle it, dispose of the contents into a toilet, then wash the potty with hot water and detergent and leave it to dry.
- Don't share towels and flannels.
- Don't prepare or serve food for others.
- If clothing or bedding is soiled, first remove any stools (faeces) into the toilet. Then wash in a separate wash at as high a temperature as possible.
- Regularly clean the toilets that you use, with disinfectant. Wipe the flush handle, toilet seat, taps, surfaces and door handles with hot water and detergent at least once a day. Keep a cloth just for cleaning the toilet (or use a disposable one each time).
- Stay off work, school, college, etc until until at least 48 hours after the last episode of diarrhoea or being sick (vomiting). Avoid contact with other people as far as possible during this time.
- Food handlers: if you work with food and develop diarrhoea or vomiting, you must immediately leave the food-handling area. For most, no other measures are needed, other than staying away from work until at least 48 hours after the last episode of diarrhoea or vomiting.
Can norovirus be prevented?
The advice given in the previous section is mainly aimed at preventing you or your child from spreading norovirus infection of the gut (gastroenteritis) to other people if you are infected. However, in general, good hygiene is essential to prevent the spread of many infections to others and to reduce your chance of picking up infections from others.
Handwashing is the most important thing that you and your child can do. In particular, always wash your hands and dry them thoroughly and teach children to wash and dry theirs:
- After going to the toilet (and after changing nappies or helping an older child to go to the toilet).
- Before preparing or touching food or drinks.
- Before eating.
If you smoke, you should also wash your hands before smoking. The simple measure of washing hands regularly and properly is known to make a big difference to the chance of developing norovirus.
Further reading and references
Guidance on infection control in schools and other childcare settings; Public Health England (September 2017)
Guidelines for the management of norovirus outbreaks in acute and community health and social care settings; Public Health England (March 2012)
Gastroenteritis; NICE CKS, July 2015 (UK access only)
Ejemot RI, Ehiri JE, Meremikwu MM, et al; Hand washing for preventing diarrhoea. Cochrane Database Syst Rev. 2008 Jan 23(1):CD004265.
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