The incidence of S. aureus bacteraemia in acute hospitals of the Mid-Western Area, Ireland, 2002-2004

Concerns about healthcare-associated infections and the global crisis in antimicrobial resistance has combined to accentuate the fears around so-called "superbugs". In Ireland there is no single agreed indicator regarded as a true measure of the level of methicillin resistant Staphylococcus aureus (MRSA) in hospitals. The objective of this study was to compare two crude measures of MRSA - the percentage of bacteraemia caused by MRSA and the incidence rate (per 1000 bed days used) of MRSA bacteraemia in six acute hospitals. We examined all blood cultures positive for S. aureus (methicillin sensitive and resistant) from 2002 to 2004 in the Health Service Executive (HSE) Mid-Western Area of Ireland. Hospital In-Patient Enquiry (HIPE) data was used to determine monthly in-patient bed days used. Of 245 patient episodes of bacteraemia, 119 were MRSA. The trends in the percentage of isolates that were MRSA and the incidence rate calculated were compared. The incidence rate appears to be a more reliable and robust indicator of MRSA in hospitals than the percentage. Despite many difficulties in interpreting indicators of MRSA they should not preclude the regular publication of data at least at regional level in Ireland.