An early analysis of healthcare workers who contracted Covid-19 suggested that twice as many caught the virus in nursing homes than in acute hospitals.
The preliminary figures were shared with unions last week following a meeting with officials but were not released as the analysis is still in progress.
A source said the analysis was based on figures that are now out of date but showed that twice as many healthcare workers in nursing homes became infected with the virus.
The figures were disclosed to trade unions following talks with Health Minister Simon Harris last week.
The Irish Nurses and Midwives Organisation has called for an inquiry into the high rates of Covid-19 among health workers, who account for more than 31pc of all confirmed cases.
The number of healthcare workers infected increased to 8,059, according to new figures released by the Health Protection Surveillance Centre last night.
Seven health care workers have died.
Siptu called on Mr Harris to release information on infection rates including the institutions in which people became infected.
Nursing homes have been among the worst hit by Covid-19, with more than 900 residents dying - 55pc of all deaths in Ireland.
Having been closed to visitors since March, nursing homes will reopen to visitors from June 15, under the Government's accelerated plans to ease restrictions. Residents will be limited to two named visitors, who will undergo temperature checks on arrival.
Chief Medical Officer Tony Holohan disclosed in a letter to the Government last week that there have been five outbreaks in prisons, with 24 people infected, none of them prisoners.
He also outlined four outbreaks in the Roma community, involving 30 cases; seven outbreaks in the Traveller community, involving 64 cases; nine outbreaks in residential centres for the homeless, involving 34 cases; and 15 in direct provision centres, involving 176 cases.
There have been 43 clusters in workplaces, with 20 of these in meat-processing plants.