Evaluating the Impact of Antibiotic Exposures as Time-Dependent Variables on the Acquisition of Carbapenem-Resistant Acinetobacter baumannii.

OBJECTIVES: To determine the time-dependent effect of antibiotics on the initial acquisition of carbapenem-resistant Acinetobacter baumannii. DESIGN: Retrospective cohort study. SETTING: Forty-bed trauma ICU in Miami, FL. PATIENTS: All consecutive patients admitted to the unit from November 1, 2010, to November 30, 2011. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Patients underwent surveillance cultures at admission to the unit and weekly thereafter. The primary outcome was the acquisition of carbapenem-resistant A. baumannii on surveillance cultures. Daily antibiotic exposures during the time of observation were used to construct time-dependent variables, including cumulative exposures (in grams and daily observed doses [defined daily doses]). Among 360 patients, 45 (12.5%) became colonized with carbapenem-resistant A. baumannii. Adjusted Cox models showed that each additional point in the Acute Physiologic and Chronic Health Evaluation score increased the hazard by 4.8% (hazard ratio, 1.048; 95% CI, 1.010-1.087; p = 0.0124) and time-dependent exposure to carbapenems quadrupled the hazard (hazard ratio, 4.087; 95% CI, 1.873-8.920; p = 0.0004) of acquiring carbapenem-resistant A. baumannii. Additionally, adjusted Cox models determined that every additional carbapenem defined daily dose increased the hazard of acquiring carbapenem-resistant A. baumannii by 5.1% (hazard ratio, 1.051; 95% CI, 1.007-1.093; p = 0.0243). CONCLUSIONS: Carbapenem exposure quadrupled the hazards of acquiring A. baumannii even after controlling for severity of illness.

Surveillance cultures growing carbapenem-Resistant Acinetobacter baumannii predict the development of clinical infections: a retrospective cohort study.

BACKGROUND: We aimed to determine the effect of the presence of carbapenem-resistant Acinetobacter baumannii in accordance with surveillance cultures on the subsequent development of clinical infections by this organism. METHODS: This retrospective cohort study was conducted at a tertiary hospital from January 2010 to November 2011. We included all consecutive patients admitted to the trauma intensive care unit, who had weekly surveillance cultures performed (from rectum, and if intubated, respiratory secretions), and without evidence of A. baumannii infections prior to the collection of the first surveillance culture. Univariable and multivariable analyses were performed using log-binomial regression. Survival analyses were performed using Cox proportional hazards. RESULTS: Three hundred sixty-four patients were included, of whom 49 (13.5%) had carbapenem-resistant A. baumannii on surveillance cultures. Patients with positive surveillance cultures had 8.4 (95% confidence interval [CI], 5.6-12.7; P < .0001) times the risk of developing a subsequent A. baumannii infection compared with patients who remained negative on surveillance cultures. Multivariable analysis showed significant associations between clinical infection and both positive surveillance cultures (relative risk [RR], 5.9 [95% CI, 3.8-9.3]; P < .0001) and mechanical ventilation (RR, 4.3 [95% CI, 1.03-18.2]; P = .05). On survival analyses, the only variable associated with the development of clinical infections was the presence of positive surveillance cultures (hazard ratio, 16.3 [95% CI, 9.1-29.1]; P < .001). CONCLUSIONS: Presence of carbapenem-resistant A. baumannii on surveillance cultures is strongly associated with subsequent development of carbapenem-resistant A. baumannii infections. Prevention efforts should be focused at limiting the acquisition of this organism during hospitalization.

Do Results of Surveillance Cultures Impact the Choice of Empirical Antibiotics Among Patients with Carbapenem-Resistant Acinetobacter baumannii Infections?

We aimed to determine whether the results of surveillance cultures were associated with use of appropriate empirical antibiotic therapy among patients with carbapenem-resistant Acinetobacter baumannii infections. We found that surveillance status was not associated with appropriate empirical antibiotic therapy (P=.36). There were significant delays to concordant therapy among surveillance-positive patients (P=.03).