Staphylococcus aureus bacteraemia (SAB) is commonly complicated by metastatic infection or relapse after treatment. Objectives. The study aim was to determine the role of bacterial, host, and management factors in development of complicated SAB. Methods. A prospectively-conducted observational study gathered data on predisposition, management and outcome of 100 consecutive SAB cases. Antibiotic susceptibilities and genetic lineage of bacterial isolates were determined. Further clinical and microbiological data were gathered on two retrospective series from 1999–2000 ( ) and 2004 ( ). Results. In the prospective cases, 27% met our definition of complicated disease. Expressed as RR and 95% CI, complicated disease was associated with diabetes (1.58, 1.00–2.48), injecting-drug use (5.48, 0.88–33.49), community-onset of symptoms (1.4, 1.02–1.92), and symptom duration hours prior to starting effective antibiotic therapy (2.10, 1.22–3.61). Uncomplicated disease was associated with the presence of a central line (0.69, 0.55–0.88) and prompt removal of a primary focus (0.71, 0.57–0.90). Neither methicillin resistance nor genetic lineage was associated with complicated disease, but methicillin resistance was associated with higher mortality. Conclusions. This study demonstrates that clinical rather than microbial factors are the major determinants of SAB outcome and underscores the importance of early treatment. 1. Introduction Staphylococcus aureus bacteraemia (SAB) is one of the commonest forms of healthcare associated infection. Among causes of bacteraemia, S. aureus is notable for how commonly it is complicated by the development of secondary foci of infection and relapse. Reported rates of complicated disease range from 12.5% to 53% depending on case definition and the population studied [1–4]. Clinical risk factors for development of complicated bacteraemia are well defined and include community onset of disease and suboptimal medical management [3, 5]. Few data exist on the importance of microbial factors, other than methicillin resistance, in determining the outcome of S. aureus infection. Previous studies have compared strain genotype from invasive and noninvasive disease [6, 7] but we are aware of only one previous study assessing the impact of genotype on outcome of bacteraemia [8]. The aim of this study was to determine the relative impact of clinical and microbiological factors on risk of developing complicated SAB. 2. Methods Brighton and Sussex University Hospitals NHS Trust (BSUH) is an 820-bed Teaching Hospital with a high SAB rate. A
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