Multidrug-resistant Acinetobacter baumannii is frequently found on Environmental Surfaces surrounding Colonized or Infected Patients

Background: Multidrug-resistant Acinetobacter baumannii (MDR-AB) is an important nosocomial pathogen with a unique ability to survive for prolonged periods of time in the environment. The role of the environment in transmission of this pathogen is incompletely understood.

Objective: To determine how often hospitalized patients with MDR-AB colonization or infection contaminate their surrounding environment and which surfaces are most frequently contaminated.

Methods:   We conducted a prospective cohort study of ICU patients known to be colonized or infected with MDR-AB at the University of Maryland Medical Center (UMMC) from October 8, 2008 to January 28, 2009. Patients with recent (within 2 months of environmental sampling) or remote (> 2 months prior to environmental sampling) history of MDR-AB positive-culture were selected at random for participation. Ten surfaces in each room were sampled. At each site, an area of approximately 10 cm² was sampled using a sterile cotton swab previously moistened with phosphate-buffered saline. Each swab was immersed in brain-heart infusion broth supplemented with 6ug/ml of imipenem which, after incubation, was subcultured to a MacConkey agar plate and a MacConkey agar plate supplemented with 6ug/ml of imipenem. Non-lactose fermenting organisms were identified as A. baumannii using CLSI criteria. Pulsed-field gel electrophoresis (PFGE) with ApaI was performed on all environmental isolates and a representative patient isolate for patients with a recent MDR-AB positive culture.

Results:   A total of 478 samples were collected from 50 rooms during the study period. In all, 9.8% (47/478) of samples were positive for growth of A. baumannii. 48% (24/50) of rooms sampled were positive at one or more sites. Supply carts (10/50, 20%); floors (8/50, 16%); infusion pumps (7/50, 14%); ventilator touch pads (5/44; 11.4%) and bed rails (5/49; 10.2%) were most commonly contaminated. 78% (39/50) of patients had a recent culture positive for MDR-AB. Patients with a recent history of MDR-AB were no more likely to contaminate their environment than patients with a remote history (51% vs. 36%, p-value = 0.50). Among the 24 patients with an environmental culture positive for A. baumannii, 20 had a recent history of MDR-AB. For these, the median (range) number of days from patient culture collection to environmental culture collection was 4 (0 to 23). In 17 of 20 instances, environmental isolates were genetically similar (identical or closely related) to the patient isolate by PFGE.  

Conclusions: For patients with MDR-AB colonization or infection, the surrounding environment is frequently contaminated, even among patients with a remote history of MDR-AB. Surfaces often touched by healthcare workers during routine patient care (e.g. supply carts, infusion pumps and ventilator touch pads) are commonly contaminated and may be a source of nosocomial spread.