Imipenem/Cilastatin/Relebactam (IMI/REL) in Treatment of CRE Infections

Inclusion Criteria: 1. Adult (\>18 years of age) patients with a KPC-producing CRE infection at any site except for isolated urinary source. Patients may be initially enrolled once identified with a CRE infection defined as resistance to any carbapenem. Any carbapenem resistance will provide an initial mechanism of identifying study eligible patients in accordance with our institutions definition of CRE for infection prevention purposes. As this study is specific for KPC-producing CRE inclusion in the study analysis will require confirmation of a KPC gene by molecular analysis of the isolate and subjects enrolled may be subsequently removed from study and excluded from analysis if molecular testing reveals their CRE isolate to be a non-KPC mechanism of resistance. Polymicrobial infections at same or different sites can also be included as long as additional gram-negative active agents aside from IMI/REL are not needed for treatment. 2. Bacterial infection with Enterobacteriaceae excluding Morganellaceae 3. Ability and willingness to give informed consent. A Legal authorized representative may be used when the patient is unable to provide informed consent. 4. Be the first episode of a CRE infection to be treated with IMI/REL. Previously treatment with IMI/REL for a KPC-containing Enterobacteriaceae infection will exclude patients from enrollment. Exclusion Criteria: 1. Receipt of more than 48 hours of effective antibiotic therapy against KPC containing infections (e.g. MVB, CZA) prior to first dose of IMI/REL being administered. 2. Infections localized to urinary source alone (bloodstream infections from urinary source will be included) 3. Infection with Morganellaceae 4. Prior serious allergic reaction to carbapenem therapy 5. Need for ongoing concomitant therapy with ganciclovir or valproic acid 6. Need for ongoing concomitant therapy with another antibiotic active against gram negative pathogens. Concomitant therapy with Vancomycin, Daptomycin, Linezolid, Clindamycin, Fidaxomicin, Nafcillin, Metronidazole, and Rifaximin will be allowed but no other antibiotic agents. 7. Pregnancy or ongoing breastfeeding. Women of childbearing age must test negative on a urine pregnancy test at time of screening for trial eligibility and remain either abstinent or use 2 forms of highly effective contraception for the duration of the IMI/REL administration during the study. 8. Inability to comply with study protocol or remain hospitalized for duration of study. 9. Life expectancy less than 72 hours in opinion of study investigators.