Nine residents of a Co Laois residential home died over the bank holiday weekend - including eight who had tested positive for coronavirus.
Those who died were aged between 66 and 84 years of age.
The 17 remaining residents at the Maryborough Centre for Psychiatry of Old Age - which is located at the St Fintan's Campus in Portlaoise - are being treated as if they are COVID-19 positive, regardless of test results or presence of symptoms.
While a number of staff are currently on sick leave, the HSE says the current staffing level is sufficient to manage the centre.
In a statement, the HSE said: "All residents have been medically reviewed by medical consultants from Portlaoise hospital.
"The HSE would like to express its sincere sympathies to the families and friends of the deceased.
"Staff at the centre are in contact with the families of the deceased and are available for support and advice."
It comes amid continuing concerns about COVID-19 cases in nursing homes and other residential institutions.
159 clusters of coronavirus cases have now been identified in nursing homes across the country, with around 60 others reported to date in other residential institutions.
Speaking on Newstalk Breakfast this morning, Amanda Phelan - Professor of Ageing & Community Nursing at Trinity College Dublin - said that the situation in nursing homes has been "chaotic".
She said: "I think [the approach is] becoming more organised in more recent days, but certainly it has been chaotic and we've seen the clusters rising.
"Nursing homes are a huge challenge in terms of infection control and actually delivering good care."