Early targeted therapy guided by rapid phenotypic antimicrobial susceptibility testing in critically ill patients with Gram-negative bacterial bloodstream infections: a retrospective cohort study

Objectives This study assessed the real-world clinical impact of rapid antimicrobial susceptibility testing (RAST) compared with conventional susceptibility testing (AST) in critically ill patients with Gram-negative bloodstream infections (GNB BSIs), focusing on early optimization of therapy and clinical outcomes in a high multidrug-resistant (MDR) setting. Methods We conducted a retrospective, observational study including adult patients with GNB BSIs who were stratified according to the susceptibility testing strategy used (RAST or conventional AST). The primary outcome was 30-day all-cause mortality. Secondary outcomes included administration of early active antimicrobial therapy, clinical failure and length of both intensive care unit (ICU) and hospital stay. Results A total of 133 patients were included (RAST: 37; AST: 96). Thirty-day mortality was observed in 4/37 patients (10.8%) in the RAST group and in 30/96 (31.3%) in the AST group (P = 0.015). Early active therapy was administered to 32/37 (86.5%) RAST patients versus 44/96 (45.8%) in the AST group (P < 0.001). Clinical failure occurred in 0/37 RAST patients versus 20/96 (20.8%) AST patients (P = 0.003). Mean ICU stay was 30.3 ± 22.9 days (RAST) versus 36.9 ± 25.6 days (AST), P = 0.17. In Cox regression analysis, RAST-guided management (HR = 0.16, 95% CI 0.04–0.62) and early active therapy (HR = 0.51, 95% CI 0.19–0.94) were independently associated with survival. Conclusions RAST may represent a valuable tool to optimize antimicrobial therapy in critically ill patients with GNB BSIs, particularly considering the increasing prevalence of MDR pathogens.