Rapid Antimicrobial Susceptibility Testing (RAST): A Quick Guide to Bacterial Sepsis Management

Background Sepsis is a life-threatening condition that remains a major global health problem. Strengthening diagnostic stewardship is vital in combating sepsis. Administration of an antimicrobial agent based on a conventional antimicrobial susceptibility testing (AST) report requires about two days after a positive blood culture. In contrast, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) Rapid Antimicrobial Susceptibility Testing (RAST) enables earlier antibiotic administration, reducing turnaround time (TAT) and improving survival. This study compares the reliability of RAST with standard AST (SAST) to establish RAST as a valuable diagnostic tool in our setting for managing bacterial sepsis. Materials and methods A prospective study (institutional ethics committee (IEC) number: RC/2023/53) was conducted in a tertiary care hospital. A total of 53 isolates were included in the study based on the inclusion criteria of monobacterial positive blood cultures. From a positively flagged blood culture bottle, Rapid Antimicrobial Susceptibility Testing (RAST) was performed, and the results of the eight-hour test were documented based on EUCAST RAST 2023 guidelines. Statistical analysis was performed using SPSS software version 29.0 (IBM Corp., Armonk, NY). Results Among the 53 isolates, Escherichia coli was the predominant isolate (49.1%, n=26), followed by Klebsiella pneumoniae (28.3%, n=15), Pseudomonas aeruginosa (11.3%, n=6), and Acinetobacter baumannii (11.3%, n=6). The average time to report by SAST was 47 hours and 45 minutes, while by RAST, it was 22 hours and 44 minutes. On comparison of the interpretative results of RAST with SAST, maximum agreement of 100% was documented for ceftazidime, ciprofloxacin, ceftazidime-avibactam, cefotaxime, and meropenem, with a kappa value of 1.000 and p-value of <0.001. We documented four minor errors (8%, n=4) in piperacillin-tazobactam, one minor error in amikacin (2%, n=1), and one major error in trimethoprim-sulfamethoxazole (2.12%, n=1). The kappa values for piperacillin-tazobactam, amikacin, and trimethoprim-sulfamethoxazole were 0.850, 0.956, and 0.957, respectively, with a p-value of <0.001. Conclusion RAST is of paramount importance in antibiotic stewardship, which has a significant impact on clinical decision-making in patients with sepsis.