487Infections Caused by Enterobacteriaceae Species following Cardiac Surgery: Impact of Polymyxin Resistance on Treatment Outcomes

Background. Mediastinitis is one of the dreaded complications post cardiac surgery resulting in high mortality rates (10% to 47%) and increased length of hospital stay and hospital costs. Thus far, no studies have described the management or outcomes of postoperative mediastinitis infections caused by carbapenem-resistant Enterobacteriaceae(CRE) resistant to polymyxins. Methods. We conducted a single center, retrospective study of cardiac surgery patients who developed mediastinitis due to CRE infections from December, 2010 to March, 2014. Patients were grouped according to whether they were susceptible (MIC ≤ 2 μg/mL) or resistant (MIC≥ 4 μg/mL) to polymyxin. Electronic medical records were reviewed for pertinent clinical and microbiological data; all isolates underwent PCR testing for the presence of the blaKPC gene. The primary outcome measure was 60 day mortality and secondary outcomes included antibiotic related length of stay (LOSAR) and duration of hospitalization. Results. In the 33 patients who developed a CRE infection during the study period, all isolates tested positive for blaKPC-2. Twenty patients (61%) were isolated with Klebsiella pneumoniae and 13 (39%) with Enterobacter species. Patients were empirically started on combination (n = 30, 91%) therapy; for targeted therapy, 10 (30%) were treated with double coverage, 14 (42%) triple coverage and 9 (27%) with four or more antibiotics. Fifteen (45%) patients were infected with polymyxin resistant strains (MIC range, 4 to ≥16 μg/mL); 18 (55%) were infected with polymyxin susceptible strains (MIC range, ≤0.5 to 2 μg/mL). Patients with a polymyxin resistant infection had a significantly higher mortality at 60 days compared to patients with a polymyxin susceptible infection (53% vs 11%, p = 0.02). No significant difference in median LOSAR was detected between groups (42 days [IQR, 28-54] vs 30 days [IQR, 16-44], p = 0.12). In addition, the length of hospitalization between groups was not significant (70 days [IQR, 48-83] vs 56 days [IQR, 40-67], p = 0.11). Conclusion. Polymyxin resistance adversely impacts patient outcomes with CRE mediastinitis infections. Further research is needed to identify optimal treatment strategies to reduce mortality associated with multi-drug resistant mediastinitis infections. Disclosures. A. Forrest, Durata Therapeutic: Consultant, Consulting fee