"We are being told all the time that staff are finding is too stressful to work in the overcrowding conditions in the emergency department and that they are opting for posts elsewhere in the hospital group".
Mr Harris said: "No effort or resource is being spared to improve this situation".
UHG was third only to University Hospital Limerick and Cork University Hospital in the grim trolley league table, with the Limerick hospital clocking almost 9,000 patients waiting on hospital trolleys over the course of past year.
While the number of people waiting for a hospital bed on trolleys in emergency departments or on wards fell to 483 on Friday, the Irish Nurses and Midwives Organisation (INMO) said the overall number recorded in the opening days of January was up 10 per cent on the same period past year.
I want to reassure the public that all the winter plan measures funded by increased investment by government, like increased access to home care, transitional care and diagnostics along with additional acute bed capacity, are being implemented to deal with the extra pressures our health service is experiencing.
A total of 55 people were on trolleys at University Hospital Limerick, while St Luke's Hospital had the highest number in the country at 57.
Varadkar said: "My apologies to any patient that has experienced a long delay".
In Dublin, the largest number of patients waiting for a hospital bed was at St Vincent's University Hospital, where 29 patients were on trolleys.
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Nursing Homes Ireland said it estimates more than 1,400 beds are available to help with hospital discharges.
At Tullamore's Midland Regional Hospital the number was 37, while Our Lady of Lourdes Hospital in Drogheda, and the Midland Regional Hospital, Mullingar both had 31 patients waiting for a bed.
The figures come as the INMO's annual figures show that nearly 100,000 people were waiting on a trolley or on a ward past year.
Ms Fogarty has also said that more robust action from management is called for to tackle the constant overcrowding problem in the emergency department at UHL.
The overall HSE figures show that overcrowding has reduced today to 438 patients, when the children's hospitals are included.
"High levels of burnout have been reported amongst nurses working in overcrowded environments", she said.
Dr Kevin Kelleher, Director of the HSE's Health Protection Surveillance Centre, said: "Influenza-like illness has increased in all age groups except in those aged 0-4 years".
"The HSE has in the last fortnight also been notified of a small number of deaths directly related to influenza (less than 10)".