ESCMID 2026
Rapid susceptibility testing falls short on outcomes in gram negative bacteremia
Clinical Takeaway: Rapid phenotypic antimicrobial susceptibility testing (AST) can shorten time to antibiotic escalation or de‑escalation, and may reduce hospital stay in select resistant infections, but routine use should be viewed primarily as a stewardship tool rather than an outcomes‑changing intervention.
In the FAST randomized clinical trial, researchers assessed whether performing rapid AST directly from positive blood cultures could improve outcomes in patients with gram‑negative bacteremia. The multinational, open‑label study enrolled 850 hospitalized adults and children at seven centers in Greece, India, Israel, and Spain—regions with high antimicrobial resistance—and the results were presented at ESCMID 2026 and published in JAMA.
Patients were randomized to rapid phenotypic AST plus standard testing (n=413) or standard susceptibility testing alone (n=437), with antimicrobial stewardship teams involved in both groups. The primary endpoint was a desirability of outcome ranking (DOOR) at 30 days, integrating survival and major complications.
The probability of a more favorable DOOR outcome with rapid testing was 48.8% (95% confidence interval, 45.3%–52.4), failing to meet criteria for superiority. Thirty‑day mortality was similar between groups (24% vs. 23%), as were ICU admission rates and overall length of stay.
Speed, however, clearly improved. Median time to antibiotic escalation or de‑escalation was 22 hours with rapid testing vs. 36 hours with standard testing. Among patients with carbapenem‑resistant organisms, time to effective therapy was markedly shorter (9.5 vs. 28 hours), and median hospital stay was reduced by about 3 days; fewer patients remained hospitalized at 30 days.
“Rapid susceptibility testing helps clinicians act sooner, but faster information alone doesn’t guarantee better outcomes,” said lead author Ritu Banerjee, MD, PhD.
Overall, FAST suggests targeting rapid AST to high‑risk resistant infections and pairing it with strong stewardship and access to effective antibiotics may offer the greatest value.
Source: Banerjee R, et al; Antibacterial Resistance Leadership Group. (2026, April 18). JAMA. Fast Antimicrobial Susceptibility Testing for Gram-Negative Bacteremia: The FAST Randomized Clinical Trial