A RARE type of influenza is on the rise in Ireland and the Health Service Executive has issued a warning to the Irish people of its effects.
The dominant form of the virus circulating is the same strain that caused people to fall ill in Australia during its last winter.
The HSE has said that the rate of patients presenting with flu-like illness to GPs shows that it is spreading.
The main strain posing a risk is the A (H3N2), which was also circulating in Ireland last winter. It was blamed for a huge outbreak in cases during the Australian winter, earning it the name 'Aussie flu'.
Dr Kevin Kelleher of the HSE said: "Influenza-like illness increased in all age groups except in those aged 0-4 years. Hospitalised cases of influenza and influenza- associated outbreaks in residential care facilities have also increased.
"Although flu is starting to circulate, flu activity remains at low levels. Prevention is better than cure, and the increase in flu activity means it is even more important to get your flu jab if you are in an at-risk group.
"Initial indications so far point to more people in at-risk groups and more healthcare workers getting the flu vaccine this year. The HSE would urge those who have not yet been vaccinated to join their peers and their colleagues in getting the flu vaccine this year."
Regardless, experts say it is unclear how effective the vaccine is against the main strain and some reports put its impact at around 20pc.
Cases of swine flu and the B strain have also been detected. There are no reported deaths from flu so far this winter.
Dr Cillian de Gascun of the National Virus Laboratory in UCD said several variants of the A (H3N2) strain had been detected here this winter and they mirrored those seen in Australia.
"The virus is not more virulent than was seen in Ireland last winter," he said, although it is possible for flu viruses to evolve over time.
He added the best defence against the virus remained the vaccine.
The outbreak is expected to continue to rise during the Christmas break due to the increase in travel and more people spending time congregated indoors over the festive period.
There were 363 patients on trolleys in A&E departments across the country yesterday, with Limerick the worst hit.