It came from Down Chunder: The norovirus strain that's wreaked havoc across the UK and made 1.2million of us ill started in Oz
Most people taken ill with norovirus caught the strain Sydney 2012
The variant was first identified in the UK in October but is already dominant
Number of cases of the winter vomiting bug rose as much as 63 per cent compared to last year

, has become the 'dominant strain' and may explain the huge rise in the number of cases.

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.

But according to recent analysis published in Eurosurveillance, 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.

Recent figures suggest that it affected 150,000 people over Christmas.

But health officials said that Sydney 2012, which has also been identified by health experts in France, New Zealand and Japan, does not cause more serious illness than other strains.

The HPA said yesterday 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 Virology Reference Department at the HPA, 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.

'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.'

Prevention: Frequent hand washing is the best way to stop contracting norovirus

Prevention: Frequent hand washing is the best way to stop contracting norovirus

He said there is no treatment for norovirus other than to let the illness take its course with symptoms normally lasting about two days.

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.

Last month hospitals said they have been so overwhelmed by people suffering from
sickness bugs that paramedics were forced to care for 999 patients.

Ambulances were left queuing outside several hospitals in Greater Manchester – including Wythenhsawe Hospital, Pennine Acute Trust's
North Manchester General, Royal Oldham, Rochdale Infirmary and Fairfield Hospital in Bury.

Symptoms include sudden vomiting, diarrhoea, or both, 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.

In the United States, the Centers for Disease Control and Prevention say norovirus causes 21 million illnesses a year, with 70,000 cases requiring hospitalisation and around 800 ending in death.

Ian Goodfellow, a scientist who has studied norovirus for 10 years, describes it as “the Ferrari of the virus world” and “one of the most infectious viruses of man”.