Methicillin-resistant Staphylococcus aureus bacteraemia and mortality in a teaching hospital

Methicillin-resistant Staphylococcus aureus (MRSA) is responsible for more than 40% of S. aureus bacteraemias in the UK and is associated with considerable morbidity and mortality. This retrospective audit examined the epidemiology of MRSA bacteraemia (MRSAB) at our institution, where the MRSAB rate has been high. A retrospective case note review was undertaken of all patients dying within 90 days of an episode of MRSAB during a 12-month period. A clinical panel classified deaths as having MRSAB as the main cause, contributing cause or having no bearing on the death. Sixty-two patients had one or more episodes of MRSAB and 30 died within 90 days. The mean age of those dying was 72 (43-96) years and of those surviving was 57 (21-87) years. MRSAB was judged to be the main or contributing cause of death in 24 cases, giving an associated mortality of 39%. All-cause mortality at 7, 30 and 90 days was 19, 40 and 48%, respectively. We investigated the minimum inhibitory contribution (MIC) to vancomycin for 79 MRSAB isolates, of which 70.8% of isolates had an MIC value of 2 mg/l. None of the isolates expressed heteroresistance to vancomycin. Five out of seven patients in whom MRSAB was the main cause of death had community onset of infection. It is unlikely that efforts to reduce delays in delivering effective antimicrobial therapy will have a major impact on mortality. Efforts to reduce the burden of MRSAB should focus on the primary prevention of bacteraemia.