Five of Northern Ireland's six largest acute hospitals did not meet approved hygiene standards when inspected, according to a new report.
The four wards examined by inspectors at the Royal Victoria Hospital in Belfast did not comply with guidelines, the Regulation and Quality Improvement Authority found.
There were also failings identified in three of four wards inspected at the Ulster Hospital in Dundonald and two of the four assessed in Belfast City Hospital.
Altnagelvin Hospital in Derry and the Craigavon Area Hospital each had one ward that did not achieve satisfactory marks from the inspectors.
All the inspections were conducted from January 2011 to March this year and were published in an RQIA overview report of hygiene and infection prevention.
All wards where compliance was not up to levels required were subjected to a follow-up inspection. Only one ward - at the Royal Victoria - also failed this secondary assessment.
Despite some of the issues flagged in the big hospitals, RQIA said overall hygiene standards and infection prevention measures were improving across the healthcare sector.
Specialist facilities, such as cancer and brain injury units, passed their inspections without the need for follow-ups.
Acute psychiatric wards and community hospitals were also found to be compliant.
RQIA Chief Executive Glenn Houston said while good hygiene practice can help reduce infection rates, there was no room for complacency.
The overview report highlighted the findings of 45 infection prevention and hygiene inspections in 85 hospital wards across 30 hospital sites in Northern Ireland.
