Five of Northern Ireland's six largest acute hospitals did not meet approved hygiene standards when inspected, according to a new report.
Four out of four wards examined by inspectors at the Royal Victoria Hospital in Belfast did not comply with guidelines, the Regulation and Quality Improvement Authority (RQIA) 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.
The Altnagelvin Hospital in Londonderry and the Craigavon Area Hospital each had one ward that did not achieve satisfactory marks from the RQIA inspectors.
All the inspections were conducted in the period of January 2011 to March this year and were published today in collated form 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.
Of the six largest acute hospitals in Northern Ireland in the period covered by the RQIA report, the Antrim Area Hospital did not require any follow-up inspections.
Despite some of the issues flagged up in the big hospitals, the 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.
Glenn Houston, RQIA chief executive, said: "RQIA commends the significant improvements in infection prevention and hygiene practice. But, 11 wards in five of the six largest acute hospitals required a further inspection."