Australian scientists have discovered three new strains of norovirus, which they say are responsible for a local outbreak of viral gastroenteritis over the last couple of months.

At the worst point of this outbreak, cases of gastro outnumbered influenza during peak flu season in some areas of Australia.

Norovirus is a single-stranded RNA virus that causes vomiting, diarrhoea, nausea, and in some cases, a temporary loss of taste.

The virus is spread through things like aerosol particles and infected faeces, and can stay on surfaces for at least seven days. As few as five virus particles are all that's needed to infect someone with norovirus.

Worldwide, the virus affects 267 million people, and causes 200,000 deaths per year, usually in patients with weakened immune systems, such as infants or the elderly.

In 2012, researchers from the University of New South Wales (UNSW) in Australia had found a strain of norovirus they named Sydney 2012, which was causing a worldwide pandemic of gastro.

"Norovirus is highly infectious and can spread through aerosol particles when people vomit," said lead researcher, Peter White.

"During the past 20 years there have been six global epidemics of norovirus, in 1996, 2002, 2004, 2006, 2009 and 2012."

But this year, the strain declined from 75 percent to 18 percent of cases in Australia, with similar trends occurring in the US and New Zealand.

And instead of one new type of norovirus rising up to take Sydney 2012's place, researchers found three new strains.

"I was surprised to find three new viruses, rather than a single one," said one of the team, Jennifer Lun.

"Two of the viruses are hybrid strains that evolved from the previous pandemic Sydney 2012 strain, while the other new strain is likely to have come from Asia."

"It occurred to me immediately that there was a potential for them to cause an increase in outbreaks this winter, because people have not been exposed to them before," she added.

The strains have been dubbed New Orleans 2009/Sydney 2012, GII.P16/Sydney 2012, and Kawasaki 308.

According to the researchers, most of the outbreaks occur in hospitals, aged care facilities, childcare centres, and cruise ships.  

"They are responsible for a big increase in the number of gastro cases in Australia in the past two months, and this new spate of infection is likely to continue to cause a wave of sick leave that will affect businesses and schools already reeling from the effects of the current influenza epidemic," White said.

"Only time will tell how widely these three new strains will spread."

The research has yet to be published in a peer-reviewed journal, so unfortunately we'll have to wait to find out more about these new strains of norovirus.

But, the researchers are still working with the Australian and New Zealand Norovirus Surveillance Network of testing laboratories, which has links with similar organisations in Europe and North America to track the global spread of these strains, and similar strains of the virus.

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