A nursing home near the border in Co Donegal has confirmed 30 Covid-19 cases.
Management at Brindley Manor Nursing Home in Convoy – 10 miles from Strabane - said most of those who tested positive displayed no symptoms while a small number showed mild symptoms.
A spokeswoman said infected residents were isolating in their rooms.
Nursing homes have accounted for more than half of the 1,810 deaths from coronavirus in the Republic since March.
The Brindley Manor spokesman said: “A family liaison officer has been appointed and will be engaging with the relatives of our residents to provide regular status updates on the health, welfare and care of their loved ones.”
She said that while still “fully operational”, the Convoy facility would remain closed to non-essential visits in keeping with Level 3 restrictions which have been put in place in the Republic.
“Our director of nursing is leading the care team at the nursing home and is working with Public Health and our medical director to ensure all appropriate measures are put in place to contain the virus."
The Republic’s Health Service Executive (HSE) confirmed that its staff were providing advice to management at Brindley Manor.
“The HSE is examining the infection control procedures and is working with the nursing home to manage the situation.”
The Donegal outbreak comes after confirmation by a Co Laois nursing home that 31 staff and residents had tested positive for Covid-19.
Kilminchy Lodge in Portlaoise – which is owned by the same parent company as Brindley Manor – said it was dealing with 21 cases among residents and 10 cases among staff.
The Republic's chief medical officer, Tony Holohan, wrote to the Irish government on Sunday to warn about the rising number of infections in nursing homes.
