The Role of Patient-to-Patient Transmission in the Acquisition of Imipenem-Resistant Pseudomonas aeruginosa Colonization in the Intensive Care Unit

Department of Pathology, Institute of Genomic Sciences, University of Maryland School of Medicine, 10 South Pine Street, Baltimore, MD 21201, USA.
The Journal of Infectious Diseases (Impact Factor: 6). 09/2009; 200(6):900-5. DOI: 10.1086/605408
Source: PubMed


Imipenem-resistant Pseudomonas aeruginosa (IRPA) is an emerging problem. The causal role of antibiotic selective pressure versus patient-to-patient transmission has not been assessed using a large cohort.
Patients who were admitted to the medical and surgical intensive care units (ICUs) at the University of Maryland Medical Center from 2001 through 2006 had multiple perianal culture samples collected. Using pulsed-field gel electrophoresis (PFGE), the number of patients who acquired IRPA as a result of patient-to-patient transmission was determined. We also analyzed a subset of patients who had a previous surveillance culture that grew an imipenem-susceptible P. aeruginosa (ISPA) and a subsequent culture that grew IRPA.
Our cohort consisted of 7071 patients. Three hundred patients were colonized with IRPA. 151 patients had positive culture findings at ICU admission, and 149 patients acquired an IRPA. Among the patients who acquired IRPA, 46 (31%) had a PFGE pattern similar to that for another isolate, and 38 (26%) were found to be colonized with an ISPA on the basis of earlier culture results. Of the 38-patient subset, 28 (74%) had identical PFGE patterns.
Our data showed that, of those cases of IRPA acquisition, 46 (31%) were defined as cases of patient-to-patient transmission, and 28 (19%) were cases of acquisition by the patients' endogenous flora.

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    • "In our study, the classical binary endogenous/exogenous scheme [12,22] is transcended by the interaction of both factors, which confirms that P. aeruginosa acquisition is complex. In the past, some molecular epidemiology studies have reported a significant role of exogenous colonization [4-7,18], whereas others have predominantly identified the role of endogenous colonization [11,13]. "
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