The implementation of rapid microbial identification via MALDI-ToF reduces mortality in gram-negative but not gram-positive bacteremia.

Our goals were to study the effect of rapid microbial identification (RMI) of positive blood culture on patient's outcome and to identify specific microbiological characteristics related to clinical benefit of RMI. This was a retrospective-cohort study of hospitalized, adult patients with bacteremia. The outcome of patients with bacteremia episodes was compared before vs. after the initiation of RMI. RMI was done by matrix-assisted laser desorption/ionization time-of-flight testing of microcolonies. The study included 1460 and 2710 cases in the pre- and post-intervention periods, respectively. There were similar rates of gram-negative, gram-positive, anaerobes, and polymicrobial infections, but higher rate of contaminants in the intervention period (39.9 vs. 43.7%, p = 0.019). The median time-to-identification decreased from 47.5 to 21.3 h (p < 0.001). Post-intervention, the median LOS declined from 10.83 to 9.79 days (p = 0.016), the rate of ICU transfer declined from 13.8 to 11.6% (p = 0.054), and the mortality rate declined from 20.9 to 18.3% (p = 0.047). The improvement in outcome variables remained statistically significant in multivariate analysis when performed for all episodes and non-contaminants but not for contaminants. The mortality declined in gram-negative bacteremia (20% vs. 15.5%, p = 0.005 in multivariate analysis) but not in gram-positive bacteremia (18.1% vs. 18.5%). RMI reduces mortality from gram-negative but not gram-positive bacteremia.