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New strain of norovirus 'dominant'

WebMD UK Health News
Medically Reviewed by Dr Farah Ahmed
norovirus molecule

10th January 2013 - A new strain of norovirus called Sydney 2012 is responsible for the majority of cases of the winter vomiting bug in England and Wales this season, scientists have confirmed.

Norovirus has been particularly virulent this winter, with an estimated 1.19 million people in England and Wales becoming ill.

Dominant strain

The Health Protection Agency (HPA) carried out genetic testing of norovirus cases. At the time cases started to rise in October, a cocktail of different strains were circulating including Sydney 2012 and New Orleans 2009. However, no one strain was dominant.

However the latest testing of recent cases, completed this week, has shown that Sydney 2012 has overtaken all the others to become the dominant strain.

The new strain does not cause more serious illness that any of the other strains in circulation.

Sydney 2012 was first seen in Australia and other cases have been identified in France, New Zealand and Japan, as well as the United Kingdom.

Diarrhoea and vomiting

Norovirus is the most common cause of diarrhoea and vomiting in the UK. It is a highly infectious form of gastroenteritis that can strike very quickly. Although it is a very unpleasant illness, it usually clears up within two to three days and has no long-term effects.

Dr David Brown, director of Virology Reference Department at the HPA says in a statement: "It is always difficult to predict the norovirus season and this year is no different.

"Noroviruses mutate rapidly and new strains are constantly emerging. At the start of the season it is normal for outbreaks to be caused by a range of different strains. However as the season progresses particular strains are more successful and become dominant.

"The emergence of a new strain does not mean that it causes more serious illness and managing outbreaks and those will the illness remains the same.

"There is no specific treatment for norovirus infection other than to let the illness take its course, with symptoms usually lasting around two days. Keeping hydrated is very important and you can take over-the-counter medicines to relieve headaches and aches and pains."

Higher infection rates

Latest figures published this week by the HPA show that there have been 4,140 laboratory confirmed cases of norovirus in England and Wales so far this season - 63% higher than for the same period last season.

Experts say that many more people will have had the stomach bug because most people do not see their doctor when they get it. It has been estimated that for every confirmed case there are around 288 unreported cases, which accounts for why more than 1.1 million people are believed to have had the winter vomiting bug in England and Wales this season.

The HPA says that between Christmas Eve and the 6th January there have been 33 suspected or confirmed outbreaks of norovirus in hospitals. Of these, 28 (85%) led to ward or bay closures.

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