Noroviruses are a group of viruses that are the most common cause of gastroenteritis (stomach bugs) in England and Wales. In the past, noroviruses have also been called ‘winter vomiting viruses’, ‘small round structured viruses’ or ‘Norwalk-like viruses’.
The virus is easily transmitted from one person to another. It can be transmitted by contact with an infected person; by consuming contaminated food or water or by contact with contaminated surfaces or objects. The infectious dose is very low, swallowing as few as 10 - 100 virus particles may be enough to cause illness.
The most common symptoms are nausea, vomiting and diarrhoea. Symptoms often start with the sudden onset of nausea followed by projectile vomiting and watery diarrhoea. However, not all of those infected will experience all of the symptoms. Some people may also have a raised temperature, headaches and aching limbs.
Symptoms usually begin around 12 to 48 hours after becoming infected. The illness is self-limiting and the symptoms will last for 12 to 60 hours. Most people make a full recovery within 1-2 days, however some people (usually the very young or elderly) may become very dehydrated and require hospital treatment.
Norovirus often causes outbreaks because it is easily spread from one person to another and the virus is able to survive in the environment for many days. There are many different strains of norovirus, immunity is short-lived and infection with one strain does not protect against infection with another strain. Outbreaks commonly occur in semi-closed environments such as hospitals, nursing homes, schools and on cruise ships, where people are in close contact with one another for long periods.
Outbreaks can be difficult to control because norovirus is easily transmitted from one person to another, its low infectious dose and because the virus can survive in the environment for lengthy periods. The most effective way to respond to an outbreak is to institute good hygiene measures such as strict adherence to hand-washing especially when handling food, after contact with infected people, and after using the toilet; disinfecting contaminated areas promptly; not allowing infected people to prepare food until 48 hours after symptoms have elapsed and isolating ill people for up to 48 hours after their symptoms have ceased.
There is no specific treatment for norovirus apart from letting the illness run its course. It is important to drink plenty of fluids to prevent dehydration.
Good hygiene is important in preventing others from becoming infected – this includes thorough hand washing after using the toilet. Food preparation should also be avoided until 48 hours after the symptoms have subsided.
There is no one specific group who are at risk of contracting norovirus – it affects people of all ages. The very young and elderly should take extra care if infected, as dehydration is more common in these age groups.
Outbreaks of norovirus are reported frequently anywhere that large numbers of people congregate for periods of several days. This provides an ideal environment for the spread of the disease. Healthcare settings tend to be particularly affected by outbreaks of norovirus. A recent study by the Agency shows that outbreaks are shortened when control measures at healthcare settings are implemented quickly, such as closing wards to new admissions within 4 days of the beginning of the outbreak and implementing strict hygiene measures.
The vast majority of people who are infected with norovirus will not have any contact with medical services. This makes formal identification of cases difficult. The HPA does obtain information on outbreaks of norovirus from hospitals and from foodborne outbreaks. The number of outbreaks varies each year.
Recent research suggest that around two million cases of norovirus occur in the community each year.
No, there are no long-term effects from norovirus.
It is impossible to prevent infection, however, good hygiene measures (such as frequent hand washing) around someone who is infected is important. Certain measures can be taken in the event of an outbreak, including the implementation of basic hygiene and food handling measures and prompt disinfection of contaminated areas, and the isolation of those infected for 48 hours after their symptoms have ceased.
Last reviewed: 27 June 2011