Implementation of the EUCAST rapid antimicrobial susceptibility test (RAST) for carbapenemase/ESBL-producing Escherichia coli and Klebsiella pneumoniae isolates, and its effect on mortality.

OBJECTIVES: With the rise in antimicrobial resistance, there is a growing demand for rapid antimicrobial susceptibility testing (RAST). In this study, we applied the EUCAST RAST method to ESBL/carbapenemase-producing Escherichia coli and Klebsiella pneumoniae isolates without using advanced identification systems and analysed the effect of this method on mortality rates Also the clinical impact of this method on patients infected with these bacteria and its effect on mortality rates were investigated. METHODS: RAST was used for clinical blood cultures containing carbapenemase/ESBL-producing E. coli and K. pneumoniae without advanced identification systems (e.g. MALDI TOF), with preliminary identification by simple diagnostic tests (predicted RAST, or p-RAST), and its categorical agreement was investigated. The impact of the method on mortality was analysed by comparing the clinical data of patients whose blood cultures were subject to p-RAST (p-RAST group, n = 49) and those who were not subject to p-RAST (non-RAST group, n = 145). RESULTS: p-RAST results were analysed based on 539 antibiotic-bacteria combinations. Total error rates at 4, 6 and 8 h of incubation were 2.9%, 3.9% and 3.8%, respectively. In the p-RAST group, patients who did not receive appropriate antibiotics (29/45, 59.1%) were switched to appropriate treatment within 8 h at the latest. In contrast, in the non-RAST group, treatment of patients who received inappropriate antibiotics (79/145, 54.5%) could be changed after at least 24 h. Mortality rates were lower in the p-RAST group than in the non-RAST group (28.6% versus 51.7%, P = 0.005). CONCLUSIONS: p-RAST can be used safely in hospital laboratories with high rates of antimicrobial resistance and can reduce mortality rates by shortening the transition time to appropriate treatment.