114 - Implementation of an Empiric Organism Specific Guidelines for Gram-negative Bacteremia in conjunction with Rapid Diagnostic Testing

Background: The objective of this study was to confirm the validity of institution specific treatment recommendations targeting organisms identified by GenMark Dx® ePlex® blood cultures identification (BCID) Gram-negative panel prior to susceptibility results.

Methods: We developed and implemented institution specific guidelines for empiric antibiotic therapy for Gram-negative organisms targeted by GenMark Dx® ePlex® BCID. We utilized blood culture antibiograms, existing evidence for the most optimal agent for each pathogen, probable resistance mechanisms and patient clinical status to create these guidelines. From December 16, 2019 through May 31, 2020, infectious diseases pharmacists reviewed all positive blood cultures; assessed compliance with guidelines and intervened as needed. The primary objective was to determine how frequently guideline recommend agents would be ineffective against targeted pathogens based on susceptibilities. Secondary objectives were compliance with guidelines and frequency of therapy escalation or de-escalation.

Results: GenMark® testing was completed on 222 cultures positive for Gram-negative rods with target organisms identification in 195 (88%) blood cultures. Two hundred and five organisms were identified; most commonly E. coli (40%) and K. pneumoniae (21%).Resistance markers were detected in 30 aerobic blood cultures; 28 CTX-M, and 2 KPC. Our institutional guideline provided appropriate empiric coverage in 93% of bacteremia episodes. The most common reason for ineffective therapy was the presence of resistance mechanisms not detected by GenMark® test (e.g. non-CTX-M extended spectrum beta-lactamases). The compliance rate with the guidelines was 55%; the most common reason for non-compliance was the use of an anti-pseudmonal beta-lactams in neutropenic patients.. The system failed to identify panel organisms in only 5 (2%) of blood cultures.

Conclusion: The institution-specific  guidelines providing empiric coverage for each organism identified by rapid diagnostic tests can aid antimicrobial stewardship efforts to de-escalate therapy while still providing effective coverage in >90% of cases.