Nosocomial outbreak of hepatitis B virus infection involving two hospitals in the Republic of Ireland.

The routes of nosocomial hepatitis B virus (HBV) transmission have changed over the years. Initiatives to prevent transfusion-associated HBV and healthcare worker-to-patient transmission have had a positive impact on these transmission routes. Recent reports of outbreaks of nosocomial HBV have implicated breaches in standard precautions as important causes of HBV transmission. This report describes a nosocomial outbreak of HBV infection in the Republic of Ireland, which occurred between January 2005 and March 2006. The outbreak was detected following identification of a case of acute HBV infection in a patient whose only risk factor was a recent surgical procedure. The extensive multi-agency investigation that followed revealed that the patient was one of five cases of acute HBV infection and that four separate transmission events between infectious cases had occurred in two different hospitals over a 15-month period. A definitive cause for each transmission event was not identified, although lapses in adherence to standard precautions, safe injection and phlebotomy practices could not be ruled out. Two secondary cases of acute HBV infection in community contacts of two of the nosocomial cases were identified. Phylogenetic analysis proved a useful tool in confirming infection with a pre-core HBV mutant and viral transmission between the seven patients. A patient notification exercise involving 1028 potentially exposed patients found no evidence of additional cases of nosocomial HBV infection. These findings highlight the importance of consistent application of standard precautions.