Microorganism Distributions and Antimicrobial Susceptibility in Community-Onset Bacteremia: A 6-Year Longitudinal Multicenter Cohort in Southern Taiwan.

Background:Prompt administration of appropriate antimicrobials has been correlated with improved prognoses in patients with bacteremia. Because the Clinical and Laboratory Standards Institute (CLSI) has numerously revised the interpretive criteria of susceptibility to numerous antimicrobials, the updated susceptibility is useful for empirical administration. Methods:In the multicenter retrospective cohort study consisting of adults with community-onset bacteremia in the emergency department (ED) during the period between January 2010 and December 2015, causative microorganisms were identified by the Vitek 2 system and prospectively collected. Antimicrobial susceptibility were respectively tested by the disk diffusion method for aerobes and the agar dilution method for anaerobes, in accordance with the contemporary CLSI criteria. Clinical information was retrospectively retrieved by reviewing the medical records. Results:Of the total 3,194 patients and 3,583 causative microorganisms, the leading source of bacteremia was the urinary tract infection (1,034 patients, 32.4%), and Escherichia coli accounted for the majority (1,332 isolates, 37.2%) of the total microorganisms. Overall, the lowest (58.2%) and highest (93.5%) susceptibility to cefazolin and piperacillin/tazobactam were, respectively, observed. In the leading five sources of bacteremia, in terms of the urinary tract infections, pneumonia, intraabdominal infections, skin and soft-tissue infections, and biliary tract infections, cefazolin or cefuroxime was only active against 49.3%-62.3% or 63.2%-74.1% of causative microorganisms, respectively. Notably, E. coli , Klebsiella species, and Proteus mirabilis (EKP) with the production of extended-spectrum beta-lactamases (ESBLs) accounted for 7.4% (142 isolates) of 1,908 EKP and 4.0% of all 3,583 microorganisms; and methicillin-resistant Staphylococcus aureus (MRSA) accounted for 37.7% (158 isolates) of S . aureus and 4.4% of all causative isolates. Conclusions:For adults with community-onset bacteremia, a low incidence (approximate 4%) of ESBL-producing EKP and MRSA among all causative microorganisms, but low susceptibility to cefazolin and cefuroxime were recognized. To achieve favorable prognoses by prompt administration of appropriate antimicrobials in EDs, our findings might offer useful information for the antimicrobial stewardship program.