New strain of winter vomiting bug blamed

The new variant of the bug, called Sydney 2012, has become the “dominant strain” and will have caused many of the cases of the recent outbreak, officials said.

In October, when the number of cases started to increase, the Health Protection Agency (HPA) performed genetic testing of norovirus strains in England and Wales. It found a “cocktail of different strains” that were circulating around the population.

However, recent analysis has shown that Sydney 2012 – first identified in Australia last year – has overtaken all others to become the dominant strain.

But officials said it does not cause more serious illness than other strains.

The HPA revealed on Tuesday that there have been 4,140 laboratory-confirmed cases of norovirus so far this season – but for every reported case, an estimated 288 are not flagged up. This means as many as 1.19 million people could have contracted the illness this season – a 63 per cent rise on the previous year.

Dr David Brown, director of the virology reference department at the HPA, said: “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.”