IRISH hospitals have been placed on alert against a new strain of the winter vomiting bug, which has reached Europe from Australia.
The norovirus stomach bug has spread to France, New Zealand and Japan and is also set to become the dominant strain in Britain.
The variant, known as Sydney 2012, is causing more cases in England and Wales than other strains.
Ireland's Health Protection Surveillance Centre (HPSC) has yet to say whether it was behind a rise in norovirus cases here.
Some 190 cases -- four times the normal number -- were recorded across the country in one week late last year.
Overall there were 1,700 reported cases of the bug -- which causes violent vomiting and diarrhoea -- although health officials believe the true figure may be far higher.
The norovirus variant was identified in a scientific paper last week and Britain's Health Protection Agency (HPA) said genetic testing showed it was now causing more cases than other strains.
Norovirus cases have risen earlier than expected this winter and while it generally does not cause serious illness, it is extremely difficult to contain.
In the US, the Centers for Disease Control and Prevention say noroviruses cause 21 million illnesses a year.
Some 70,000 of these require hospitalisation and around 800 end in death. Scientist Ian Goodfellow, who is an expert in norovirus, described it as "the Ferrari of the virus world" and "one of the most infectious viruses of man".
Ireland suffered a huge spike in the number of cases before Christmas, with thousands laid low by the virus, but the rates had fallen last week and only 29 cases were recorded the week before last.
However, the figure masks the true extent of the illness as most cases are not reported with many people choosing not to attend their GPs or local hospital.