Methods: At an urban tertiary teaching hospital in Philadelphia we surveyed Gram-negative blood isolates and their susceptibilities from Safety Surveillor and AECIS, a Cerner based EMR. Data was collected on Gram-negative bloodstream isolates from inpatients and their susceptibility to five different antibiotics: Cefepime (CEF), piperacillin-tazobactam (P-TZ), ciprofloxacin (CIP), tobramycin (TOB) and imipenem (IMI).
Results: We reviewed 545 Gram-negative blood stream isolates. We excluded Gram-negative isolates from cultures with multiple organisms, Gram-negatives that were obligate anaerobes, and cultures that were obtained after 72 hours of admission. A total of 348 Gram-negative isolates which met these criteria were retrospectively studied for susceptibility using double antibiograms. Our results showed that IMI monotherapy had the highest likelihood of empiric coverage compared to any monotherapy or combination therapy. We also excluded IMI and looked at the results of the remaining antibiotics; we found that only for CIP monotherapy did adding another class of antibiotic improve the likelihood of empiric coverage (p= 0.04). IMI also was noted to have the highest likelihood of empiric coverage for ESBL/CRE isolates and also for patients admitted to the intensive care or step-down units (ICU/SDU). However, for Pseudomonas isolates (n = 22), monotherapy or combination therapy with CEF, TOB, PIP-TAZ had a better likelihood of empiric coverage than IMI or CIP. For this particular isolate, adding another antibiotic to IMI or CIP did improve the likelihood of empiric coverage.
Conclusion: For the Gram-negative bloodstream isolates we surveyed, IMI monotherapy had a better likelihood of empiric coverage than any other mono or combination therapy for isolates overall, ESBL/CRE isolates and isolates from patients admitted to the ICU/SDU. However, for Pseudomonas isolates, when IMI or CIP monotherapy was considered, adding another class of antimicrobials increased the likelihood of empiric coverage.