Background: Colonization by carbapenem-resistant Acinetobacter baumannii (CRAB) is a risk factor for the development of clinical infections by this organism. We aim to explore the impact of antibiotic exposures on the acquisition of CRAB.
Methods: This retrospective cohort from 11/1/10 to 11/30/11 included consecutive patients to the trauma intensive care unit (TICU), whom underwent rectal [and tracheal if intubated] surveillance cultures upon unit admission and weekly thereafter. Patients positive on admission surveillance were excluded. Hazard ratios for the acquisition of CRAB were calculated using time dependent and time-independent antibiotic exposures. Time independent variables were: 1. binary variables (received versus not) determined for each antibiotic and for all antibiotics (any antibiotic received versus none) and 2. total sum of grams and 3. total sum of DDDs received during the observation period (for each antibiotic and for all [DDDs]). Time dependent antibiotic exposures included 1. time after the first day of each antibiotic (0 vs. 1), 2. daily cumulative exposure (daily sum in grams or DDDs), and 3. the immediate hazard after a single day of antibiotics. APACHE on admission, age, and gender were also analyzed using Cox models.
Results: A total of 364 patients were analyzed; 60 patients developed CRAB infections, and 49 patients had positive surveillance cultures. Gender and APACHE were independently associated with acquisition of CRAB. Analyzing antibiotic exposures as time-independent variables showed that any carbapenem exposure doubled the hazard of colonization. Using time-dependent variables, carbapenem quadrupled the hazard of CRAB colonization (HR: 3.9; p=0.0007). Single DDD of carbapenem was associated with 4.6% higher hazard for colonization. The immediate impact of a single day of carbapenem on the hazards of developing colonization is shown in Figure 1.
Conclusion: Exposure to carbapenems increased the risk of CRAB colonization. The impact of this effect was maximum on the first day of exposure and decreased over time.
R. Latibeaudiere, None
S. Tarima, None
L. S. Munoz-Price, None