A new strain of the winter vomiting disease norovirus has spread to France, New Zealand, and Japan from Australia and is set to become the dominant strain in Britain.
It is unclear if the new strain of the virus, known as Sydney 2012, has reached Ireland.
However, the Health Protection Surveillance Centre last month recorded an increases in norovirus cases.
In mid-December, 115 cases were recorded in one week.
The norovirus variant was identified in a scientific paper last week. Britain’s health protection agency said genetic testing showed it was now causing more cases in England and Wales than other strains.
Sydney 2012 does not carry worse symptoms than others but, like other norovirus strains, it can cause violent and projectile vomiting, diarrhoea, and sometimes fevers, head-aches, and stomach cramps.
Norovirus cases have risen earlier than expected this winter in Britain, across Europe, Japan, and other parts of the world.
Although norovirus mos-tly causes just a few days of sickness, it is responsible for millions of infections every year and is notorious for its ability to evade control.
In the US, the Centers for Disease Control and Prevention say norovirus causes 21m illnesses a year, with 70,000 cases requiring hospitalisation and about 800 ending in death.
Ian Goodfellow, a scientist who has studied norovirus for 10 years, described it as “the Ferrari of the virus world” and “one of the most infectious viruses of man”.
For every laboratory-confirmed case, scientists estimate there are 288 un-reported cases, since the vast majority of people affected do not go to a doctor.
Norovirus does not usually cause serious illness, but it is very easily spread. People who contract it can be infectious for 48 hours after they recover.
Now that I've recovered from the vomitting bug, it's the son's turn!— sinlotus (@sinlotus) January 7, 2013
The principal symptoms are nausea, vomiting, and diarrhoea and generally begin very suddenly with nausea followed by projectile vomiting.
A little later watery diarrhoea may develop as well. Symptoms will usually last only a day or two but can, occasionally last longer.
In any year at least 1% — and in high activity years up to 5% — of the population can expect to be affected by this virus meaning that between 1,000 and 5,000 people could fall ill with norovirus per week during a busy period.
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