Diagnosis and management of Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia (SAB) is common. Around 8000 cases occur per year in Australia, of which 60% are hospital- or healthcare-associated. Risk factors for SAB include injectable drug use, haemodialysis, indwelling vascular catheters and immunosuppression. Metastatic infection develops in up to one-third of patients with SAB, with joints and heart valves being the most commonly affected sites. Community-acquisition,persistent fever, positive blood cultures after 48 h of treatment and the presence of embolic lesions correlate with the presence of complicated SAB (i.e. high risk of endocarditis and/or other metastatic complications). All patients require careful clinical evaluation to exclude endocarditis and other metastatic foci. Echocardiography,preferably transoesophageal echocardiography, should be performed to exclude endocarditis. Most patients with SAB, and all with features of complicated SAB, require prolonged intravenous antibiotic therapy (at least 4 weeks), but a subgroup with good prognostic features may be suitable for shorter intravenous therapy (2 weeks). Penicillinase-resistant penicillins (e.g.flucloxacillin) are the agents of choice for SAB with methicillin-sensitive strains. Vancomycin or first-generation cephalosporins are alternatives but have lower antimicrobial activity than flucloxacillin. However, vancomycin remains the therapy of choice for SAB due to methicillin-resistant strains. Combination therapy with gentamicin may be useful for the first few days of treatment in selected patients, but otherwise there are few data to support the use of combination regimens in SAB. Newer agents such as linezolid and quinupristin/dalfopristin may have a role in selected patients, especially in SAB due to S. aureus strains with reduced susceptibility to vancomycin.