1609. Epidemiology and Susceptibility to Imipenem/Relebactam of Gram-Negative Pathogens from Patients with Lower Respiratory Tract Infections – SMART United States 2017-2018

BACKGROUND: Relebactam (REL) inhibits class A and C β-lactamases and was approved in the US combined with imipenem (IMI) and cilastatin for complicated urinary tract and intraabdominal infections. Using isolates collected as part of the global SMART surveillance program in the US, we evaluated the activity of IMI/REL against gram-negative pathogens (GNP) from patients with lower respiratory tract infections (LRTI), including a comparison of isolates from ICU and non-ICU wards. METHODS: In 2017-2018, 27 US hospitals each collected up to 100 consecutive aerobic or facultative GNP from LRTI patients per year. MICs were determined using CLSI broth microdilution and breakpoints. RESULTS: Among 3878 GNP isolates from LRTI, the most common species collected were P. aeruginosa (Psa, 33.3%), K. pneumoniae (10.9%), E. coli (10.4%), and S. marcescens (6.9%). Susceptibility of GNP is shown in the table. IMI/REL inhibited 93% of Psa and Enterobacterales, which included 174 isolates of Morganellaceae that are not expected to be susceptible to IMI or IMI/REL. S. marcescens also showed low susceptibility to IMI, with improved but still reduced activity upon addition of REL. IMI/REL inhibited 83% of all GNP combined, 7-18 percentage points higher than the comparator β-lactams. Of the tested comparators, only amikacin exceeded the activity of IMI/REL. Only Psa showed substantial differences in susceptibility between isolates from ICU (n=486) and non-ICU wards (n=611), with 63.4% and 70.2%, respectively, susceptible to IMI, 71.6/78.7% to cefepime, and 64.2/73.3% to piperacillin/tazobactam (P/T). Susceptibility to IMI/REL was high in both settings (91.4/93.6%). Among Enterobacterales, susceptibility was generally similar in ICU and non-ICU wards (IMI/REL, 92.5% in both settings; IMI, 86.3 and 87.1%, respectively; cefepime, 89.9/89.0%; P/T, 88.7/87.4%). Table [Image: see text] CONCLUSION: Although resistance rates have frequently been reported to be higher in ICU than non-ICU wards, this pattern was seen in the current study only among Psa isolates. IMI/REL showed activity >90% against both Enterobacterales and Psa from both ward types. These in vitro data suggest that IMI/REL could provide an important treatment option for patients with LRTI in the US, including those in ICUs. DISCLOSURES: Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Katherine Young, MS, Merck & Co., Inc. (Employee, Shareholder)Merck & Co., Inc. (Employee, Shareholder) Mary Motyl, PhD, Merck & Co, Inc (Employee, Shareholder) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)