Methicillin-resistant Staphylococcus aureus bacteraemia diagnosed at hospital admission: distinguishing between community-acquired versus healthcare-associated strains.

BACKGROUND Methicillin-resistant Staphylococcus aureus (MRSA) infections diagnosed at hospital admission are often referred to as community-acquired. This designation may include MRSA strains previously acquired in a healthcare setting (healthcare-associated) as well as those that have emerged from community-based S. aureus strains. METHODS To understand further the epidemiology of MRSA from the community, a case-control study was performed. During 1997-2002, 254 patients with and without MRSA bacteraemia at hospital admission were studied. RESULTS All patients with MRSA bacteraemia in the first 24 h of hospital admission had a recent exposure to a healthcare setting: true community-acquired MRSA was not detected. Independent risk factors for healthcare-associated MRSA bacteraemia, defined as MRSA bacteraemia in the first 24 h of hospital admission among patients with a recent exposure to a healthcare setting or intervention, included previous MRSA infection or colonization (OR = 17, P < 0.001), cellulitis (OR = 4, P = 0.006), presence of a central venous catheter (OR = 3, P < 0.001) and skin ulcers (OR = 3, P = 0.007). CONCLUSIONS In this study, MRSA bacteraemia diagnosed in the first 24 h of hospital admission represented healthcare-associated MRSA strains and not true community-acquired strains. The clinical characteristics associated with healthcare-associated MRSA bacteraemia can assist clinicians in targeting measures to prevent cross-transmission and may help to streamline empirical vancomycin therapy.