Integration of MALDI-TOF MS into antimicrobial stewardship pathways and inappropriate empiric antibiotic therapy in gram-negative bloodstream infections: a quasi-experimental before–after study

This study compared inappropriate empiric antibiotic therapy (IEAT) rates in Gram-negative bloodstream infections (GN-BSIs) before and after the stepwise integration of rapid matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) result interpretation into antimicrobial stewardship pathways. This single-center, uncontrolled quasi-experimental study was conducted between 2019 and 2025. The study included four periods: pre-intervention (Pre-IP) and three intervention periods (IP-1 to IP-3). MALDI-TOF MS was routinely used for pathogen identification throughout all study periods; the interventions targeted its reporting and integration into the stewardship workflow. Interventions were implemented sequentially: infectious diseases and medical microbiology team education, monitoring of Gram stain and MALDI-TOF MS reporting times and regular weekly feedback to the microbiology team (IP-1), direct communication of results to primary physicians in real time via short message service (SMS) (IP-2), integration of an antimicrobial stewardship team into the reporting pathways and the use of local algorithms for empiric antibiotic therapy (IP-3). MALDI-TOF MS and Gram stain reporting times and IEAT rates were monitored for each period. A total of 1688 GN-BSIs were included. IEAT was given to 27.4% ( n = 463) of the patients. IEAT rates were higher in GN-BSIs related to multidrug-resistant (MDR) (33.8% vs. 22.7%, p < 0.001) and carbapenem resistant (47.2% vs. 16.5%, p < 0.001) pathogens. The number of Systemic Inflammatory Response Syndrome (SIRS) criteria (odds ratio [OR] 0.73, 95% confidence interval [CI]: 0.66–0.82), infectious diseases consultation (OR 0.40, 95% CI: 0.31–0.53), Gram stain reporting time (OR 1.02, 95% CI: 1.01–1.03), MALDI-TOF MS reporting time (OR 1.014, 95% CI: 1.009–1.018), GN-BSI with E. coli (OR 0.43, 95% CI: 0.32–0.57) and GN-BSI with MDR bacteria (OR 1.87, 95% CI: 1.47–2.38) were independently associated with IEAT. Across the intervention periods, MALDI-TOF MS reporting time and time to infectious diseases consultation decreased ( p < 0.001), antibiotic revision rates increased ( p < 0.001) and IEAT rates were significantly lower in later periods ( p < 0.001). Our study suggests that accelerated diagnostic workflows based on routine MALDI-TOF MS combined with an antimicrobial stewardship team were associated with significantly lower IEAT rates in GN-BSIs.