Clinical impact of EUCAST rapid antimicrobial susceptibility testing on empirical therapy in bloodstream infections: a real-world observational study.

PURPOSE: This study assessed the impact of EUCAST's Rapid Antimicrobial Susceptibility Testing (RAST) on empirical therapy and its clinical usability in routine bloodstream infection management.

METHODS

This retrospective single-center, observational study compared two four-month periods before and after RAST implementation (Feb-May 2023 vs. Feb-May 2024) at Oldenburg Medical Center. Patients with monomicrobial bloodstream infections due to Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, or Acinetobacter baumannii were included.

PRIMARY OUTCOME: duration of empirical antimicrobial therapy.

SECONDARY OUTCOMES: turnaround time and categorical agreement between RAST with VITEK 2, including major errors (ME) and very major errors (VME). Surrogate-based interpretation was used for ATU results, particularly for piperacillin-tazobactam.

RESULTS

In total 126 patients were included (66 in 2023, 60 in 2024). After RAST, empirical therapy duration was significantly shorter (40.5 h vs. 73.3 h, p < 0.001). Median time to RAST result was 15.8 h, significantly shorter than by VITEK 2 (33.9 h, p < 0.0001), reducing time to first susceptibility result by 9.6 h (p < 0.00001). Concordance with VITEK 2 was excellent: 100% for cefotaxime, meropenem, and piperacillin-tazobactam, 96.4% for ceftazidime, 95.2% for ampicillin. ATU results occurred mainly for piperacillin-tazobactam and were partly resolved through surrogate-based interpretation.

CONCLUSION

RAST significantly shortened empirical therapy duration and accelerated susceptibility reporting with high agreement to VITEK 2. However, antibiotic-specific uncertainty and incomplete translation of early results into therapeutic action indicate that the clinical impact of RAST depends on structured interpretation and integration into antimicrobial stewardship workflows.