It found some improvements after a re-inspection in Mayo University Hospital
The health watchdog HIQA is criticising three hospitals for failing to put basic measures in place to prevent the spread of infection.
In its latest tranche of reports, it has highlighted concerns over Croom, Letterkenny and Castlebar hospitals.
It raised particular concerns over dialysis facilities in Letterkenny University Hospital - where neither of the isolation rooms had a separate ventilation system.
"Neither of the two isolation rooms in the main dialysis unit had a separate ventilation system, nor were there anterooms for putting on and removing personal protective equipment", it found.
"These rooms were small in size and only one of these single rooms had an en-suite toilet.
"One of the rooms had two doors, of which one opened directly into the main unit; this is not in line with best practice", it found.
But it also found that since the last inspection, the hospital had invested in "improvement and upgrade works" in some clinical areas, and has an ongoing patient area renovation programme.
It also said a leak around a large window - which extended over multiple levels on the front of the hospital building - had been addressed.
In the orthopaedic ward, three isolation rooms with en-suite facilities had been renovated and refurbished - and there were plans for further improvement of patient areas and ancillary rooms.
"The hospital had also invested in new equipment including commodes, bedside lockers, bedside tables and drip stands. A mattress and bed replacement programme was in place so that damaged mattresses could be replaced. There were regular checks of mattress integrity," HIQA said.
At Croom Hospital in Limerick, inspectors found "infrastructural deficiencies" relating to sanitary facilities that were not fully addressed.
"It was reported that funding had been sought to upgrade these facilities. Similar to observations during the 2014 inspection, the underside of the shower basin grids were heavily stained and unclean," HIQA said.
It added that ceiling fans remained in use in the inpatient wards at the time of the inspection.
"Fans are not generally recommended for use in clinical areas as their use can increase the risk of transmission of Healthcare Associated Infections."
While the inspector also observed that the door of an isolation room was open. It was also critical of Croom's reprocessing of reusable medical devices.
"The infrastructure of current facilities do not comply with the Health Service Executive Code of Practice for Decontamination of Reusable Invasive Medical Devices, and are not in compliance with the national standards", it found.
While in Mayo University Hospital HIQA found that as renovation works were taking place, measures to prevent dust from entering the orthopaedic ward were not in place.
"The standard of patient equipment hygiene in the orthopaedic ward was not in line with national infection control standards", it said.
It also said that "opportunities for improvement of environmental hygiene" were seen in the renal dialysis unit.
However, a re-inspection two months later found "significant improvement" in relation to the construction and renovation works.
But it said "significant scope for improvement was again identified" in relation to environmental hygiene in both the orthopaedic ward and renal dialysis unit during the re-inspection in July.
All inspections were unannounced.