A man being treated for Legionnaires' Disease in Tallaght Hospital, Dublin, remained in a critical condition last night.
The hospital said the man, who was transferred to the hospital from the North Eastern Health Board region, is being treated in isolation.
The patient originally presented with the disease at Our Lady's Hospital in Navan on August 16th.
The North Eastern Health Board, in a statement issued yesterday, said it immediately began investigating the source of his illness.
"Test results in relation to possible sources of infection are awaited," it said.
It added that this was "a single isolated case" of the potentially deadly Legionnaires' Disease.
While the disease is rare in the Republic two deaths have already been reported from the disease so far this year.
The most recent was that of Mrs Ena Kiely who died in April after contracting the disease while a patient at Waterford Regional Hospital where she was being treated for an underlying chronic medical condition.
The South Eastern Health Board appointed an independent team to investigate the circumstances surrounding her death and they are due to report soon.
It is believed Mrs Kiely (61), from Kilmacthomas, Co Waterford, contracted the disease by inhaling water vapour from a shower head in the hospital which was contaminated with legionella bacteria.
Mr Bob Brophy (69), from Dublin died at Beaumont Hospital, also in April, after contacting the disease after inhaling droplets of water from a hot-tub at a house he was viewing for his daughter.