656. Prioritizing Gram-Negative Bacteremia (GNB) Cases for Rapid Detection by β-Lactam Resistance (BLR) and Patient Outcomes

Background GNB is associated with significant morbidity and mortality. The availability of rapid diagnostic tests (RDTs) provides an opportunity to improve outcomes. Our goal was to review GNB and its empiric treatment at our center in order to devise rational approaches to diagnostic stewardship and use of RDTs. Methods All patients with GNB from 2010 to 2018 were evaluated. BLR was defined by 2019 CLSI breakpoints; phenotypes are shown in Table 1. Results A total of 2795 GNB cases were included (Table 2); 57% occurred within the first 24 hours of hospitalization and 29.3% in the ICU. The median length of stay (LOS) was 12 days; 17.2% of patients were re-admitted within 30 days. Fourteen- and 30-day mortality rates were 13.7% and 19.5%, respectively. Rates of death were higher (30 days; 26.3% vs. 17.1%; P < 0.001) and median LOS longer (17 vs. 11 days; P < 0.001) among patients with BLR compared with susceptible GNB. Thirty-day mortality rates were highest for CRE (30.1%) and BLR P. aeruginosa (BLR-Pa; 32.8%, Figure 1). 47.7% of BLR GNB were non-CRE/ESBL, which demonstrated higher mortality rates than CRE/ESBL (30 days; 27.6% vs. 21.2%; P = 0.048). Most common empiric regimens prescribed were piperacillin–tazobactam (TZP; 50.3%), cefepime (FEP; 24.2%), carbapenem (9.3%), or other agents (16.2%). 21.6% of GNB patients received inactive empiric treatment (IET). Empiric TZP (21.9%) was more likely to be inactive than FEP (17.5%; P = 0.05), but not a carbapenem (20.7%; P = NS). 57.6% of patients with inhibitor-resistant Enterobacteriaceae (IRE) received TZP empirically. Receipt of IET was associated with higher rates of death (30 days; 22.5% vs. 16.7, P = 0.03) and longer LOS (14 vs. 11 days; P < 0.001) than receipt of active ET. Rates of IET varied by pathogen (Figure 1). Conclusion IET is common against BLR GNB and associated with poor pt outcomes, highlighting the potential for RDTs and diagnostic stewardship teams (DSTs) to improve care. Genotypic RDTs detect most CRE/ESBL, but may miss nearly 50% of BLR GNB cases at our center. BLR-Pa and IRE are pathogens associated with prolonged LOS, and high rates of IET and death. These pathogens could be detected earlier by phenotypic RDTs and prioritized by DSTs to optimize early treatment regimens. Disclosures All authors: No reported disclosures.