Norovirus is a virus which causes more episodes of infectious diarrhoea and vomiting (gastroenteritis) in Britain than any other infection. The illness caused by Norovirus had been known as "winter vomiting" for years before the virus was identified.

Symptoms usually only last for two or three days and it does not cause any permanent adverse effects.

The main symptoms are diarrhoea, vomiting, and abdominal pain, but you may also experience headaches, low-grade fever, and nausea.

The cause is infection with a norovirus. Previously known as Norwalk-like viruses, there are three genogroups that affect humans. It is a highly infectious disease and is spread by:

• eating food that is contaminated
• touching a surface that has been contaminated with the virus and then spreading it from your fingers to your mouth
• close contact with someone who is infected

The incubation period is usually 12 to 48 hours.

Diagnosis will normally be assumed because of the symptoms and especially the prevailing circumstances, such as other cases in the area.

Specimens are rarely taken to prove the diagnosis in an individual case, as this is not of any practical value.

Treatment is essentially as for diarrhoea and vomiting.

When to call the doctor

Norovirus is very infectious and you should stay in, avoiding contact with other people, and most times you will not need to see the doctor. If, however, the member of the household who has the infection has a pre-existing serious condition which complicates things or causes reduced immunity, or if you concerned about their condition, phone for medical advice.

Norovirus is very infectious. You start shedding the virus from the onset of symptoms and are unlikely to continue shedding the virus longer than three days from then. However, it is possible to shed the virus before symptoms develop and up to two weeks after recovery.

• Avoid unnecessary contact with other people
• Wash hands thoroughly with soap and running water
• Alcohol based gels are ineffective against norovirus and are not a substitute for washing with soap and water
• Care with preparing food: wash all fruit and vegetables carefully
• Do not prepare food for other people while infected and for at least 48 hours after getting over the infection
• Open windows and air the room after vomiting - aerosolized vomit droplets are infectious
• Decontaminate any surfaces which may be contaminated, using a bleach based household cleaner or diluted bleach in solution (care must be taken to follow the manufacturer's instructions)
• Immediately wash contaminated clothes, bedding or towels at the highest temperature that is allowed and for a maximum wash, using detergent

• Diarrhoea and vomiting
• Centers for Disease Control and Prevention