Risk factors and outcome of polymicrobial bacteremia: A retrospective cohort study

Background: Recent data regarding polymicrobial bacteremia (PMB) are lacking. Objectives: To characterize risk factors as well as clinical, microbiological, and prognostic patterns of patients with PMB in a modern hospital setting. Methods: A single center retrospective study including all patients diagnosed with PMB during 2013 was conducted. PMB was defined as two or more organisms cultured from the blood of the same patient within 72 hours. Patients with monomicrobial infections served as controls. Results: There were 135 episodes (2% of all bacteremia episodes) of true PMB among 123 patients during the study period. Recent invasive procedures (odds ratio [OR] 3.59, 95% confidence interval [95%CI] 1.41-9.12, P= 0.006) and foreign bodies (OR 1.88, 95%CI 1.06-3.33, P= 0.04) were risk factors for PMB when compared with 79 patients with monomicrobial bacteremia. Central-line-associated infections were the most common infection source among patients with PMB (n=34, 28%). Enterobacteriaceae were the most commonly implicated pathogen (n=95, 77%). Non-fermenting Gram-negative bacilli were significantly more common than previously reported (n=55, 45%). Although crude 30-day mortality was higher (48% vs. 33%) in PMB patients, adjusted mortality was comparable in the two groups. Conclusions: PMB rate in our cohort was considerably lower than in previous reports. Central-line-associated infections were more common than classic PMB sources. Mortality remained high. Strategies for early identification and better care for these patients should be pursued.