Association of Once-Daily MALDI-TOF MS Identification with Antibiotic Appropriateness and First-Modification Patterns...

Background: Blood cultures are frequently obtained in the emergency department (ED), yet organism identification and subsequent antibiotic optimization commonly occur after hospital admission. Inappropriate empiric therapy remains common and is associated with adverse outcomes. MALDI-TOF MS can shorten the time to organism identification; however, real-world effectiveness may depend on laboratory cadence and stewardship support, and evidence for once-daily batch workflows without active antimicrobial stewardship is limited. Method: We performed a retrospective before-after cohort study at a tertiary medical center in central Taiwan, comparing positive blood cultures (PBCs) obtained in the ED before MALDI-TOF MS implementation (1 May-31 July 2018; conventional identification) and after implementation (1 September-30 November 2018; MALDI-TOF MS). Primary endpoints were appropriate antibiotic therapy at 24, 48, and 72 h after the first PBC report. Secondary endpoints included timing, location, and classification (escalation vs. de-escalation) of the first antibiotic modification. Results: After exclusions, 323 unique PBCs were analyzed (182 pre-implementation; 141 post-implementation). Baseline characteristics and clinical outcomes were similar, including in-hospital mortality (14.8% vs. 14.9%). Time to the initial positive report (Gram stain) and the final report (identification with antimicrobial susceptibility testing) did not differ significantly between periods. Appropriate antibiotic use at 24/48/72 h was comparable (75.3% vs. 76.6%, 82.4% vs. 80.1%, and 86.3% vs. 84.4%). The timing and pattern of the first antibiotic modification were also similar. In a secondary stratified analysis, patients modified before culture positivity had higher acuity and worse outcomes. Conclusions: Once-daily MALDI-TOF MS implementation was not associated with improved antibiotic appropriateness or modification patterns in ED bacteremia without active real-time stewardship oversight. Higher-frequency processing and real-time stewardship linkage may be required to translate faster diagnostics into timely therapeutic action.