Community-onset bacteraemia of unknown origin: clinical characteristics, epidemiology and outcome

Bacteraemia of unknown origin is prevalent and has a high mortality rate. However, there are no recent reports focusing on this issue. From 2005 to 2011, all episodes of community onset bacteraemia of unknown origin (CO-BSI), diagnosed at a 700-bed university hospital were prospectively included. Risk factors for Enterobactericeae resistant to third-generation cephalosporins (3GCR-E), Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus spp, and predictors of mortality were assessed by logistic regression. Out of 4,598 consecutive episodes of CO-BSI, 745 (16.2 %) were of unknown origin. Risk factors for S. aureus were male gender (OR 2.26; 1.33–3.83), diabetes mellitus (OR 1.71; 1.01–2.91) and intravenous drug addiction (OR 17.24; 1.47–202); for P. aeruginosa were male gender (OR 2.19; 1.10–4.37) and health-care associated origin (OR 9.13; 3.23–25.83); for 3GCR-E was recent antibiotic exposure (OR 2.53; 1.47–4.35), while for enterococci, it was recent hospital admission (OR 3.02; 1.64–5.55). Seven and 30-day mortality were 8.1 % and 13.4 %, respectively. Age over 65 years (OR 2.13; 1.28–3.55), an ultimately or rapidly fatal underlying disease (OR 4.15; 2.23–7.60), bone marrow transplantation (OR 4.07; 1.24–13.31), absence of fever (OR 4.45; 2.25–8.81), shock on presentation (OR 10.48; 6.05–18.15) and isolation of S. aureus (OR 2.01; 1.00–4.04) were independently associated with mortality. In patients with bacteraemia of unknown origin, a limited number of clinical characteristics may be useful to predict its aetiology and to choose the appropriate empirical treatment. Although no modifiable prognostic factors have been found, management optimization of S. aureus should be considered a priority in this setting.