Bloodstream Polymicrobial Infections: Do They Have Any Impact On Mortality?

Background: Polymicrobial bloodstream infections (pBSI) can bring about a worse clinical evolution than monomicrobial ones (mBSI). As this fact has not been clearly proved, a deeper study of pBSI could contribute to elucidate the issue. The objective of the present study is to describe the epidemiology, clinical features and outcome of pBSI compared to mBSI. Methods & Materials: A retrospective matched case-control study with a ratio 1:3 among patients with pBSIs and mBSI was conducted. The case group was composed by patients aged > 18 years with pBSI. A control group of patients with mBSI were matched by age and sex with the others. Demographic information, underlying condition, microbiological data, and outcomes were collected for further analysis. Chi square analysis and Kruskal-Wallis test were used for categorical and for continuous variables, respectively. Results: From January 2015 to December 2016, a total of 108 episodes of bacteremia were included (23.14% pBSI and 76.86% mBSI). Intraabdominal infections (p = 0,816) and respiratory tract infections (p = 0,009) were more likely associated with pBSI. A combination of E. coli, Pseudomonas aeruginosa, Klebsiella spp. and Acinetobacter baumannii was predominant among pBSI. Among mBSI, Klebsiella spp., E. coli or Pseudomonas aeruginosa predominated. Among all the bacteria isolated, 40% of pBSI and 48% of mBSI were multi drug resistant (MDR) gram-negative (p = 0,074). Appropriate empirical antimicrobial treatment was administered to 83.3% of pBSI, and to 78.3% of monomicrobial BSI. The overall 30-day mortality rate of the pBSl group and the mBSI group showed no difference (32% vs 30%; p = 0,886). Conclusion: Intraabdominal and respiratory tract infections are the most common source of pBSI. The prevalence of MDR gram negative bacteria and the rate of appropriate empirical antimicrobial treatment were similar in both groups. The results of the present study do not support previous findings regarding higher mortality in pBSI compared to mBSI.