Doctors, chemists and hospital casualty departments throughout Ireland are said to be "inundated" by patients with serious colds and flu-like symptoms.
Some chemists have had problems supplying medicines while a spokeswoman for An Post said the company had been "decimated" by flu, with staff levels down by 30-40 per cent in some areas.
Mr Seamus Dooley, laboratory manager of the Virus Reference Laboratory at UCD, said they had established that a H3N2 strain of the common influenza A virus was in circulation here. Those who had the flu injection would be protected against it, while others would have built up resistance.
Doctors said the flu-like symptoms should take four or five days to clear for most people. They advised "rest, fluids, and paracetamol". But they warned against taking too much paracetamol as even a minor overdose could cause liver damage.
In Dublin, Dr Pearse Phelan of the Doctors on Duty service, which acts as support for general practitioners who are off, said calls had trebled from 200 to 600 a day. He had seen 70 patients on Monday, 60 on Sunday, 50 on Saturday.
Ms Mary Rose, divisional nursing manager at Beaumont Hospital in Dublin, said up to 20 people there last night were awaiting admission at its casualty department, while another 15 had yet to be seen. "We are running out of trolleys and ambulances are queuing up outside," she said.
A spokeswoman at Tallaght hospital casualty said it had been "pressure, pressure, pressure, with a capital P . . . huge pressure since St Stephen's Day. I'll tell you something, it's rough."
She was "ashamed to say" that delays there were now "in double figures". People were lying "everywhere", in corners and corridors.
In Northern Ireland, 11 patients at the Mater Hospital in Belfast spent much of yesterday on trolleys waiting for beds, while a spokeswoman for the Antrim, Whiteabbey and Mid-Ulster hospitals was quoted as saying they were "under extreme pressure."
Dr Dermot Nolan of the Irish College of General Practitioners said the outbreak was having "a major effect on consultation rates" at doctor's surgeries while hospitals were "inundated.".
The Dubdoc group, which supplies an out-of-hours medical service related to St James's Hospital, was flat out, he said. Delays at St James's casualty were such that "up to 25 per cent of patients were leaving without being seen".
Mr Brendan Quinn, president of the Irish Pharmaceutical Union, said his chemist shop in Gort, Co Galway, had a 20 per cent increase in patient numbers during December, and it was continuing. Reports of shortages were "widespread" from chemists all over the State, he said.
Dr Terry Maguire of the Ulster Pharmaceutical Society, said "the system is at breaking point trying to supply medicine to patients".
Ms Marie Hogan, vice-president of the IPU, said she had intended opening her shop in Limerick for two hours on New Year's Day. Instead she had to stay open for eight.
The spokeswoman for An Post said 130 of its workers in Dublin and 35 workers in Galway were ill yesterday.
