Bed occupancy and incidence of Methicillin-resistant Staphylococcus aureus infection in an intensive care unit

Methicillin-resistant Staphylococcus aureus (MRSA) incidence and workload as reflected by daily bed occupancy were assessed retrospectively over a 12-month period in a mixed adult ICU. All MRSA positive results were retrieved from the Microbiology Department; patients with MRSA were divided into those whose admission swabs were positive and those whose specimens subsequently became positive. There were 619 admissions, 48 of which had MRSA on admission (7.8% incidence) and 16 new MRSA infections in ICU (total incidence 10.3%). The frequency of MRSA acquisition was significantly higher on days when more than seven beds were occupied (0.0090 vs 0.0059 new acquisitions per patient per day, respectively, p = 0.015). In this well staffed but physically small unit local routes of infection transmission may be relevant.