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Norovirus: cases of winter vomiting bug estimated to be up 63% on last year Norovirus: new strain may be behind 63% increase in cases
(about 1 hour later)
A new strain of norovirus is responsible for most of the recent cases of the winter vomiting bug, health experts say. Most people contracting the norovirus winter vomiting bug are being hit by a new strain, which may explain the huge increase in cases this year, health officials have said.
The new variant, called Sydney 2012, has become the dominant strain and will have caused many of the cases of the recent outbreak, officials said. The new strain of norovirus, called Sydney 2012, was first detected in the UK in October but has now become "the dominant strain", the Health Protection Agency (HPA) said on Tuesday.
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. They found a "cocktail of different strains" that were circulating around the population. HPA genetic testing of patients in England and Wales affected by norovirus last October, when it began circulating again, identified Sydney 2012 as one of a number of strains that were affecting a growing number of patients, which also included another strain called New Orleans 2009. At the time none of what the HPA called a "cocktail of different strains" was dominant, the HPA said.
However, recent analysis has shown that Sydney 2012 – first identified in Australia last year – has overtaken all others to become the dominant strain. While other strains are still in circulation, Sydney 2012 is responsible for the majority of recent cases in England and Wales. But the latest testing of the most recent outbreaks, completed this week, shows that Sydney 2012 has overtaken all others to become the dominant strain.
But health officials said that Sydney 2012, which has also been identified in France, New Zealand and Japan, does not cause more serious illness than other strains. Sydney 2012 was first seen in Australia – and named for the place it was first identified. It has also been seen in France, New Zealand and Japan, the agency said in a statement confirming the new strain's presence here for the first time.
The HPA said on Tuesday 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% rise on the previous year. The HPA stressed that Sydney 2012 did not affect patients worse than previous strains of norovirus, which is highly contagious. "This new strain does not cause more serious illness than others, and the methods of managing cases and outbreaks are the same for any strain of norovirus. These measures include washing the hands thoroughly and regularly, particularly after using the toilet and before eating," it said.
Dr David Brown, director of the HPA's virology reference department, said: "It is always difficult to predict the norovirus season and this year is no different. Noroviruses mutate rapidly and new strains are constantly emerging. However, an HPA spokeswoman said the mutation of the virus may be why 63% more people have been hit by norovirus so far this winter than during the same period last year. Until now experts had been baffled by the fact that the virus peaked unusually early this winter.
"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. "Dr David Brown [the director of the agency's virology reference department] says that it may explain … why the epidemic has come early this year," she said.
"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." But it does not definitively explain the surge. "There are no definitive answers about this. David says that it can lead to an increase in cases but it doesn't necessarily do that," she added.
Norovirus is highly contagious and can be transmitted through contact with an infected person or contaminated surfaces and objects. It is known to spread rapidly in closed environments such as hospitals, schools and nursing homes. HPA data released on Tuesday showed that an estimated 1.19 million people in the UK – a big increase on last year – have been affected by norovirus so far this winter in a surge that has closed dozens of hospital wards and also caused outbreaks in some schools, workplaces and cruise ships. Some 150,000 people were struck by it over the festive season alone. It usually affects about 3 million people between October and April.
Symptoms include sudden vomiting, diarrhoea, a temperature, headache and stomach cramps. The bug usually goes away within a few days. Although people can suffer from norovirus at any time of the year, activity increases in the winter months, with most cases seen between January and March. The new strain was the subject of a scientific paper published in the journal Eurosurveillance on 3 January, which called it Sydney 2012.
"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", said Dr Brown.
"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," he added.
The HPA does not know at what point after October the Sydney 2012 strain became the dominant type of norovirus circulating, the spokeswoman said.
During the last two weeks of 2012, the HPA confirmed 529 cases of norovirus. But for every reported case, an estimated 288 are not flagged up. The bug has swept the country and has led to the closure of dozens of hospital wards. During the past two weeks, 33 hospital outbreaks have been reported.