Using Prior Culture Results to Improve Initial Empiric Antibiotic Prescribing: An Evaluation of a Simple Clinical Heuristic.

BACKGROUND A patient's prior cultures can inform the subsequent risk of infection from resistant organisms, yet prescribers often fail to incorporate these results into their empiric antibiotic selection. Given that timely initiation of adequate antibiotics has been associated with improved outcomes, there is urgent need to address this gap. METHODS In order to better incorporate prior culture results in selection of empiric antibiotics, we performed a pragmatic prospective hospital-wide intervention: (1) Empiric antibiotic prescriptions were assessed for clinically significant discordance with most recent methicillin-resistant staphylococcus aureus (MRSA) surveillance swab, previous cultures for extended-spectrum beta-lactamases (ESBLs), and most recent culture for a Gram-negative (GN) organism; (2) If discordant, an antimicrobial stewardship pharmacist provided recommendations for alternative therapy. The impact was analyzed using a quasi-experimental design comparing two 9-month periods (pre and post-intervention) at a large academic tertiary care institution. RESULTS Clinically significant discordance was identified 99 times in the pre-intervention period and 86 times in the intervention period. The proportion of patients that received concordant therapy increased from 73% (72/99) in the control group to 88% (76/86) in the intervention group (p=0.01). The median time to concordant therapy was shorter in the intervention group (25 vs 55 hrs; p<0.001 aHR=1.95 (95%CI 1.37-2.77, p<0.001). The median duration of unnecessary vancomycin therapy was reduced by 1.1 days (95% CI 0.5 - 1.6 days, p<0.001). CONCLUSIONS This intervention improved prescribing, with a shorter time to concordant therapy and increased proportion of patients receiving empiric therapy concordant with prior culture results. Use of unnecessary vancomycin was also reduced.