Rapid bloodstream infection testing can cut antibiotic decision time by more than half, yet failed to move the needle on overall survival in a large international trial, according to findings published in JAMA and presented at the European Society of Clinical Microbiology and Infectious Diseases congress in Munich.
The FAST trial enrolled 899 patients with gram-negative bacteremia across seven hospitals in Greece, India, Israel and Spain, randomizing them to either standard antimicrobial susceptibility testing—which takes three days or longer—or a rapid method that delivers results in six to eight hours by testing blood directly from positive cultures. Though the primary endpoint showed no superiority for rapid testing, with a 48.8% probability of being better than standard care in a composite outcome of survival without deleterious events at 30 days, secondary analyses revealed meaningful shifts in care. Time to first antibiotic escalation or de-escalation dropped from a median of 36 hours with standard testing to 22 hours with rapid testing across the full cohort, and was even more pronounced in resistant subgroups: cephalosporin-resistant infections saw decisions accelerate from 35 to 12 hours, while carbapenem-resistant cases jumped from 47 to 13 hours.
Among patients infected with carbapenem-resistant organisms, the impact extended beyond the lab. Hospital stays shortened by a median three days, and the proportion remaining hospitalized at 30 days fell from 28% with standard testing to 15.1% with rapid testing. All-cause mortality, ICU admission and acquisition of new multidrug-resistant organisms remained statistically similar between groups, underscoring that faster diagnostics alone did not translate into lives saved in this trial.
Yet the economic modeling paints a different picture of potential. A first-of-its-kind health economic analysis by the Office of Health Economics projects that if fast identification and antimicrobial susceptibility testing were deployed early in the sepsis care pathway across G7 nations, it could prevent 84,400 sepsis cases and save 36,200 lives annually in the United States alone. The model estimates similar proportional gains across Canada, France, Germany, Italy, Japan and the United Kingdom, arguing that earlier, targeted antibiotic intervention—before clinical deterioration—could avert the cascade that drives sepsis mortality and excess costs.
This tension between trial results and projection highlights a central challenge in sepsis management: diagnostics must be paired with timely action to realize benefit. As Ritu Banerjee, MD, PhD, first author of the FAST trial and professor of Pediatrics at Monroe Carell Jr. Children’s Hospital at Vanderbilt, noted, “Although we did not find differences in clinical outcomes like mortality, we did find that use of the rapid test led to faster antibiotic treatment changes targeting the resistant pathogens.” She added that trends toward shorter length of stay and more successful discharge at 30 days in highly resistant subgroups “provide proof of concept that use of rapid tests that can quickly identify resistance, and when implemented together with antibiotic stewardship team review, can improve timely targeted treatment for patients with sepsis.”
The caveat remains cost. Rapid testing carries a higher price tag than conventional methods, a factor that influenced the trial’s design in low-resource settings where antimicrobial resistance is prevalent. Banerjee emphasized that better diagnostics are only one component of a broader strategy to combat antibiotic resistance, requiring integration with stewardship programs and systemic reforms to ensure equitable access.
Last time a similar diagnostic promise met mixed trial results was with procalcitonin-guided antibiotic stewardship in the early 2010s, where biomarker-guided algorithms reduced antibiotic use without harming outcomes—but adoption stalled amid questions about real-world implementation and cost-effectiveness, a pattern that could repeat if rapid AST fails to demonstrate clear mortality benefit in broader populations.
Does rapid testing actually save lives in sepsis?
The FAST trial found no statistically significant difference in 30-day mortality between rapid and standard testing groups (24.2% vs 22.7%), but modeling suggests earlier use could prevent tens of thousands of sepsis cases and deaths annually in high-income countries by enabling faster, targeted antibiotic therapy before clinical deterioration.
Why did the trial show faster antibiotic decisions but no mortality benefit?
Rapid testing shortened time to antibiotic escalation or de-escalation by 14 hours on average, yet mortality remained unchanged, possibly because the window for intervention in sepsis is narrower than the gain achieved, or because concomitant factors like comorbidities and delayed presentation limited the impact of faster diagnostics alone.
What role does antibiotic stewardship play in realizing the benefit of rapid tests?
Rapid AST was associated with improvements in more timely antibiotic modifications and targeted antibiotic therapy in certain subsets of patients, more frequent guidance from antimicrobial stewardship teams, and greater acceptance of stewardship recommendations.
The study authors noted that rapid testing’s value emerges when paired with stewardship review, enabling faster, more precise treatment adjustments—particularly for resistant infections—though this synergy did not reach statistical significance for mortality in the trial.
Is rapid testing cost-effective for health systems?
While rapid testing is more expensive per test than conventional methods, the Office of Health Economics analysis projects substantial net savings for G7 health systems through reduced sepsis incidence, shorter hospital stays and avoided complications, contingent on early deployment and integration with stewardship programs.
