An 80-year-old woman has been on a trolley for more than 70 hours in the emergency department at University Hospital Galway.
The Irish Nurses and Midwives Organisation said there were 544 patients on trolleys in emergency departments, or on wards, waiting admission to a bed in hospitals around the country.
Figures show that there 37 patients on trolleys at the Galway hospital, but the worst affected was University Hospital Limerick with 53 patients.
Staff in UHG's emergency department say ten people have been waiting more than 40 hours to be admitted to hospital, while a further 14 patients have been on trolleys for more than 24 hours.
The Health Service Executives figures put the number of patients on trolleys at 396, with GUH the worst affected.
Unlike the INMO figures, the TrolleyGar figures do not give the number of patients placed on wards, who are waiting for admission for a bed, having already been admitted from an emergency department.
Tallaght Hospital has converted eight beds from a facility normally used for children, to an adult unit to cope with overcrowding.
The unit was being used as a short stay paediatric observation unit. There are no children in the unit where the adult patients are now.
The hospital said it is a temporary measure and necessary as all adult escalation areas and beds are in use.
The beds in question will revert to the paediatric service in due course.
Meanwhile, the HSE has estimated that around 20,000 people had flu or flu symptoms in the last week and that flu levels may have peaked, or may do so next week.
Assistant National Director for Public and Child Health Dr Kevin Kelleher said there had been a threefold increase in flu levels in the last week, which he described as significant.
He said that four weeks into the flu season, there was probably another four to six weeks of flu activity.
The hospital overcrowding crisis is putting pressure on ambulance services as paramedics say they have to wait to discharge patients to emergency departments.
Speaking on RTÉ's Morning Ireland, paramedic Michael Dixon said that in some cases the situation is leading to delays in attending emergency calls.
Mr Dixon, who is also Chairman of the National Ambulance Service Representative Association, said there have been times when paramedics have waited up to an hour-and-a-half for patients to be admitted to acute hospitals.
He said the spike in usage, as for example at Cork University Maternity Hospital or University Hospital Limerick, means when there are no available beds in the emergency department "there's a knock-on effect and ambulances have to wait to discharge their patients. The knock-on effect is on ambulance services then".
Mr Dixon said the real issue in the spike is the need for health services at this time of year.
"We are never prepared for it. We talk about it every year. Realistically for next winter we should start planning now."
To ease overcrowding, more than 80 patients were transferred from public hospitals to private facilities in Dublin and Cork in the past week.
HSE CEO Tony O’Brien apologised to patients waiting on trolleys describing it as unacceptable, but warned that unless planned health reforms go ahead, what is being experienced now will look like a picnic in a few years' time.
Mr Dixon, meanwhile, has called for a liaison officer between the ambulance groups and hospitals, and said questions need to be asked such as "are we giving the service to the right hospital?".
He added: "For example if the CUMH in Cork is busy, we have the opportunity to use other hospitals in the area. Some patients can be treated in community hospitals, not everyone needs an A&E."