ARTICLE Impact of nosocomial polymicrobial bloodstream infections on the outcome in critically ill patients S. Sancho & A. Artero & R. Zaragoza & J. J. Camarena & R. González & J. M. Nogueira Received: 7 August 2011 /Accepted: 20 November 2011 /Published online: 14 December 2011 # Springer-Verlag 2011 Abstract The aims of this study were to compare the clinical and microbiological characteristics from patients with poly- microbial bloodstream infections (BSI) to those from patients with monomicrobial BSI and to determine their influence on the prognosis. A prospective study was conducted on 371 nosocomial BSI in an intensive care unit (ICU). Seventy- five (20.2%) of them were polymicrobial. The mean APACHE II score at the onset of bacteremia in polymicrobial and monomicrobial BSI were 17.7±6.6 and 18.9±7.5, respec- tively (p 0 0.228). Severe sepsis and septic shock were present in 68.0% and 50.6% of polymicrobial BSI and in 73.9% and 55.1% of monomicrobial BSI, respectively (p 0 0.298 and p 0 0.494, respectively). The length of stay and the length of stay post-infection were significantly longer in patients with polymicrobial BSI. APACHE II score at the onset of BSI, high-risk microorganisms, and septic shock were predictors of related mortality, but polymicrobial BSI and inadequate em- pirical antimicrobial treatment were not. Our findings suggest that the clinical and microbiological characteristics of poly- microbial BSI are not different from monomicrobial BSI, and polymicrobial BSI do not have any influence on the related mortality. However, they occurred in patients with a longer length of stay in the hospital and were associated with longer stays in the hospital after the episode of BSI. Introduction Nosocomial bloodstream infections (BSI) are among the most frequent and severe infections in intensive care unit (ICU) patients, especially in those with severe sepsis and septic shock [1–4]. A great majority of polymicrobial BSI have a nosocomial origin, but the proportion of polymicro- bial BSI in series of nosocomial infections in critical ill patients are relatively low [5, 6] and recent studies on these infections are scarce [7]. The differences in the clinical and microbiological features between monomicrobial and poly- microbial BSI in critically ill patients are not well estab- lished, and, most importantly, their impact on the prognosis remains unclear [8]. The aims of this study were: (1) to ascertain the clinical and microbiological characteristics of polymicrobial noso- comial BSI in an ICU, in comparison with hospital-acquired monomicrobial bacteremias and (2) to determine their influ- ence on global and related mortality in hospital and on the length of stay. Materials and methods Study location and patients The study was carried out in a university-affiliated urban teaching hospital with 600 beds: Hospital Universitario Dr. Peset in Valencia, Spain. During a period of 136 months (October 1998 to February 2010), all adult medical-surgical ICU patients with nosocomial-acquired bloodstream infection were prospectively analyzed. Study design A prospective cohort study was used. Its characteristics have been previously described [9]. We collected demographic, clinical, microbiological, hospital course, and outcome data. Patients were segregated according to the polymicrobial S. Sancho (*) : A. Artero : R. Zaragoza : J. J. Camarena : R. González : J. M. Nogueira Hospital Universitario Dr. Peset, Valencia, Spain e-mail: sancho_sus@gva.es Eur J Clin Microbiol Infect Dis (2012) 31:1791–1796 DOI 10.1007/s10096-011-1503-8