Six people have died in a private nursing home in Co Donegal within the last two weeks, with five deaths in the last five days.
The HSE has said the deaths, which occurred in Nazareth House, Fahan, Co Donegal, may have been as a result of a respiratory type illness.
“The HSE is fully investigating the matter and all appropriate treatment and control measures have been put in place,” it said.
“All residents in the nursing home are currently receiving either active or preventative treatment.”
Samples have also been sent to the National Viral Reference Laboratory for examination.
In a statement, Minister for Health James Reilly and Minister for Older People Kathleen Lynch expressed their condolences over the deaths.
They said they are being kept fully informed as the situation evolves.
Dr Darina O’Flanagan of the Health Protection Surveillance Centre said tonight that the HSE held an outbreak control team meeting today.
Dr O’Flanagan said the HSE has been in the nursing home investigating the cases.
She said it does not yet know the cause of the illness.
Dr O’Flanagan said that some of the patients who died were admitted to hospital last week and that the initial investigations on a bacterial cause were negative.
She said it looks as if this may be a viral illness, but it may turn out to be influenza. She added that there are other possible viruses or even possible bacterial causes.
Laboratory tests and swabs were taken today and the HSE hopes to have results sometime tomorrow evening.