2175. Rapid Detection of Carbapenemase Producing Organisms Directly from Blood Cultures Positive for Gram-Negative Bacilli

BACKGROUND: The rapid detection of carbapenemase-producing organisms (CPOs) directly from blood cultures (BC) positive for Gram-negative bacilli (GNB) may accelerate the appropriate treatment of at-risk patients. Our objective was to evaluate the performance of two commercial assays in the rapid detection of CPOs directly from BC positive for GNB. METHODS: BC positive for GNB, taken from patients within the Calgary Health Zone over a 3 month period, were tested for the presence of CPOs with βCARBA® and NG-Test® CARBA 5. A subset of sterile BC samples was seeded with multi-drug-resistant (MDR) GNB. BC were incubated using the Bact-Alert™ system. Positive BC from clinical and seeded samples was tested directly with βCARBA and CARBA 5 from BC pellets processed for direct testing using an ammonium chloride lysis and wash method. Sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) were calculated with 95% confidence intervals for binomial proportions. RESULTS: 65 samples were tested (30 clinical, 35 seeded). Seeded samples included 1 GES, 4 IMP, 6 KPC, 1 co-producing KPC and NDM, 9 OXA, 4 VIM, 5 NDM, and 5 non-CPO carbapenem-resistant organisms. βCARBA had a sensitivity, specificity, NPV and PPV of 100% (88.4% - 100%), 65.7% (47.8–80.9%), 100%, and 71.4% (61.3%–79.8%), respectively. CARBA 5 had a sensitivity, specificity, NPV and PPV of 90.0% (73.5%–97.9%), 100% (90.0%–100%), 92.1% (80.0%–97.2%), and 100%. When excluding GES, which is known not to be detected by CARBA 5, sensitivity and NPV increased to 93.1% (77.2%–99.2%) and 93.1% (78.0%–98.1%), respectively. False negatives for βCARBA occurred with 1 VIM-1 and IMP-14. CONCLUSION: This study demonstrates that the detection of CPOs directly from positive BC can be accurately achieved. βCARBA had excellent sensitivity but suffered from poor specificity. CARBA 5 had good sensitivity and specificity but is unable to detect certain CPOs. Testing positive BC directly using βCARBA and/or CARBA 5 may be useful in rapidly detecting CPOs. Results of direct testing from the CARBA5 assay would quickly identify patients amenable to treatment with avibactam combination compounds. DISCLOSURES: All authors: No reported disclosures.