Norovirus

Authored by Dr Colin Tidy , Reviewed by Dr Hannah Gronow on | Certified by The Information Standard

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.

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).

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.

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.

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.

Note: severe dehydration can be fatal unless quickly treated because the organs of your body need a certain amount of fluid to function.

For more information about symptoms, including dehydration, see the separate leaflets called Diarrhoea and Acute Diarrhoea in Children.

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.

Children

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 becoming 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.

Adults

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 becoming 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. 

There is no special medication to treat norovirus. The aim is to make sure that you or your child have 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. For further information see the separate leaflets called Diarrhoea and Acute Diarrhoea in Children

Medication

Antibiotic medicines are not needed to treat norovirus. It is a viral infection so antibiotics will not be effective. See the separate leaflet called Diarrhoea Medicine for further information

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 you 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 gut (intestinal) 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 with your doctor or practice nurse if you are unsure of what to do if you are taking other medicines and have gastroenteritis.

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.

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

When to worry about diarrhoea
How to avoid tummy bugs

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