Evaluating the Practical Impact of Fast Microbiology on the Treatment of Bloodstream Infections: Real-World Evidence from a High-Complexity Infectious Disease Center

Background/Objectives: Bloodstream infections (BSIs) are a major cause of morbidity and mortality, particularly when delays in pathogen identification hinder timely and targeted antimicrobial therapy. Rapid diagnostic tests (RDTs) accelerate microbiological identification, yet their clinical impact remains heterogeneous across different healthcare settings. This study aimed to evaluate the real-world effect of implementing FAST microbiology, a diagnostic workflow that integrates RDTs into conventional blood culture processing, on diagnostic timeliness, antimicrobial decision-making, and patient management in a hospital specializing in complex infectious diseases. Methods: We conducted a quasi-experimental study comparing non-FAST and FAST workflows over a 24-month period, including 166 adult patients with sepsis admitted to ICU and non-ICU units, accounting for 231 BSIs. Microbiological outcomes, treatment dynamics, time to targeted therapy, and key clinical endpoints were compared between non-FAST and FAST groups. Results: FAST microbiology significantly reduced the time to initiation of targeted therapy across clinical settings. No statistically significant differences were observed in hospital length of stay, overall mortality, or 28-day mortality between the two groups. Baseline clinical severity, age, and comorbidity burden remained the main determinants of clinical outcomes. Conclusions: These real-world findings support the integration of rapid diagnostics into existing antimicrobial stewardship frameworks by improving diagnostic timeliness and supporting earlier microbiologically guided therapeutic decisions. However, the results also highlight that accelerating diagnostics alone may not be sufficient to improve survival in critically ill patients with complex infectious diseases, where outcomes are predominantly driven by patient- and disease-related factors.