Up to 5,000 people in the State have been struck down by the winter vomiting disease so far this year, it has emerged.
The virus, which is still affecting patients at hospitals in Roscommon and Clonmel, has had huge cost implications for a number of health boards, with staff accounting for up to one-third of those who became infected.
Health boards are now compiling accurate figures for the amount the virus cost them and will be seeking to recoup the unexpected spending from the Department of Health.
A spokesman for the Department of Health said a number of health boards had submitted estimates of their costs associated with the bug. These included estimates from the Western and Southern Health Boards of €1 million each, he said.
The department, he confirmed, had now asked other health boards to submit their estimates.
The east, south and south-east were among the regions worst hit by the virus, but it is not yet clear why so many became infected with a virus this year which would normally affect a small number in other years.
The first cases this year were reported in Northern Ireland, following an outbreak in Scotland. It is believed the virus then spread southwards, with the first outbreak in the Republic occurring at a hospital in Co Louth, resulting in the closure of a ward for some days in January.
Cases were also reported by the National Disease Surveillance Centre among Irish passengers returning from skiing holidays in Andorra at the end of January.
Figures collated by the magazine Medicine Weekly show more than 1,000 people were affected in the Eastern Regional Health Authority Area, followed by 829 in the Southern Health Board area and 800 in the South Eastern Health Board region. More health board staff than patients became infected in the south-east.
The outbreak resulted in serious disruption at some hospitals which had to cancel elective surgery.
Mr Seamus Dooley, laboratory manager of the National Virus Reference Laboratory, said hospitals and institutions had been "caught unprepared by the virus" and had found it difficult to cope.
The illness usually lasts no longer than 48 to 72 hours but is highly infectious, particularly because of the projectile vomiting associated with onset. It is estimated that 20 million virus particles may be sent into the air during a vomiting attack.