Carbapenems are considered the treatment of choice for Acinetobacter baumannii infections. Many facilities implement preventive measures toward only carbapenem-resistant A. baumannii (CRAB). However, the independent role of the carbapenem resistance determinant on patient outcomes remains controversial. In a 6-year analysis of adults with A. baumannii bloodstream infection (BSI), the outcomes of 149 CRAB isolates were compared to those of 91 patients with carbapenem-susceptible A. baumannii . In bivariable analyses, CRAB BSIs were significantly associated with worse outcomes and with a delay in the initiation of appropriate antimicrobial therapy (DAAT). However, in multivariable analyses, carbapenem resistance status was no longer associated with poor outcomes, while DAAT remained an independent predictor. The epidemiological significance of A. baumannii should not be determined by its resistance to carbapenems.

Background: Risk factors and outcomes associated with carbapenem-resistant Enterobacteriaceae (CRE) acquisitions are derived primarily from cohorts consisting of carbapenemase-producing (CP) strains. Worldwide epidemiology of non-CP-CRE is evolving, but controlled epidemiological analyses are lacking. Methods: A matched case-case-control investigation was conducted at Shamir (Assaf Harofeh) Medical Center, Israel, on November 2014–December 2016. Noncarbapenemase-producing CRE (as defined by the US Clinical and Laboratory Standards Institute Standards) carriers were matched to patients with non-CRE Enterobacterales and to uninfected controls (1:1:1 ratio). Matched and nonmatched multivariable regression models were constructed to analyze predictors for acquisition and the independent impact of carriage on multiple outcomes, respectively. Representative isolates were whole genome sequenced and analyzed for resistome and phylogeny. Results: Noncarbapenemase-producing CRE carriers (n = 109) were matched to the 2 comparative groups (overall n = 327). Recent exposure to antibiotics (but not specifically to carbapenems), prior intensive care unit admission, and chronic skin ulcers were all independent predictors for non-CP-CRE acquisition. Acquisitions were almost exclusively associated with asymptomatic carriage (n = 104), and despite strong associations per univariable analyses, none were independently associated with worse outcomes. Genomic analyses of 13 representative isolates revealed polyclonality, confirmed the absence of carbapenemases, but confirmed the coexistence of multiple other genes contributing to carbapenem-resistance phenotype (multiple beta-lactamases and efflux pumps). Conclusions: Noncarbapenemase-producing CRE acquisitions are primarily associated with asymptomatic carriage, specifically among prone populations with extensive recent exposures to antibiotics. The prevalent mode of acquisition is “emergence of resistance” (not “patient-to-patient transmission”), and therefore the role of stewardship interventions in reducing the spread of these therapeutically challenging pathogens should be further explored.

Vancomycin-resistant enterococci (VRE) are a growing health problem, and uncertainties exist regarding the optimal therapy for bloodstream infection due to VRE. We conducted systematic comparative evaluations of the impact of different antimicrobial therapies on the outcomes of patients with bloodstream infections due to VRE. A retrospective study from January 2008 to October 2010 was conducted at Detroit Medical Center. Unique patients with blood cultures due to VRE were included and reviewed. Three major therapeutic classes were analyzed: daptomycin, linezolid, and β-lactams. Three multivariate models were conducted for each outcome, matching for a propensity score predicting the likelihood of receipt of one of the therapeutic classes. A total of 225 cases of bacteremia due to VRE were included, including 86 (38.2%) cases of VR Enterococcus faecalis and 139 (61.8%) of VR Enterococcus faecium . Bacteremia due to VR E. faecalis was more frequent among subjects treated with β-lactams than among those treated with daptomycin or linezolid. The median dose of daptomycin was 6 mg/kg of body weight (range, 6 to 12 mg/kg). After controlling for propensity score and bacteremia due to VR E. faecalis , differences in mortality were nonsignificant among the treatment groups. Therapy with daptomycin was associated with higher median variable direct cost per day than that for linezolid. This large study revealed the three therapeutic classes (daptomycin, linezolid, and β-lactams) are similarly efficacious in the treatment of bacteremia due to susceptible strains of VRE.