Impact of a Laboratory-Developed Phenotypic Rapid Susceptibility Test Directly From Positive Blood Cultures on Time to Narrowest Effective Therapy in Patients With Gram-Negative Bacteremia: A Prospective Randomized Trial.

Background: Antimicrobial susceptibility testing (AST) is often needed prior to antimicrobial optimization for patients with gram-negative bloodstream infections (GN-BSIs). Rapid AST (rAST) in combination with antimicrobial stewardship (AS) may decrease time to administration of narrower antibiotics. Methods: This was a prospective, nonblinded, randomized trial evaluating the impact of a phenotypic rAST method vs conventional AST (cAST) in hospitalized patients with GN-BSI and source control. The primary outcome was time to narrowest effective therapy. Results: Two hundred seventy-four patients were randomized and 205 underwent analysis (97 cAST, 108 rAST). Median (interquartile range [IQR]) time to susceptibility results was 23 hours shorter in the rAST group (cAST: 62 [59-67] hours vs rAST: 39 [IQR, 35-46] hours; P < .001). Median (IQR) time to narrowest effective therapy was similar between groups (cAST: 73 [44-138] hours vs rAST: 64 [42-92] hours; P = .10). Median (IQR) time to narrowest effective therapy was significantly shorter in a prespecified subgroup of patients not initially on narrowest therapy and during AS working hours (cAST: 93 [56-154] hours vs rAST: 62 [43-164] hours; P = .004). Significant decreases were observed in median (IQR) time to oral therapy (cAST: 126 [76-209] hours vs rAST: 91 [66-154] hours; P = .02) and median (IQR) length of hospital stay (cAST: 7 [4-13] days vs rAST: 5 [4-8] days; P = .04). Conclusions: In patients with GN-BSI, rAST did not significantly decrease time to narrowest effective therapy but did decrease time to oral antibiotics and length of hospital stay. Rapid AST using existing microbiology platforms has potential to optimize patient outcomes.