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MRSA Screening in The ICU: Nares and Skin Are Not Enough
Abstract & Commentary
By David J. Pierson, MD, Editor, Professor, Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, is Editor for Critical Care Alert.
Synopsis: In this single-center cohort study, 7% of ICU patients were colonized with MRSA on admission. In 34% of the positive cases, MRSA was detected by throat or rectal swabs but not by cultures of the anterior nares and other keratinized areas.
Source: Batra R, et al. Intensive Care Med. 2008 (May 24); epub ahead of print
This prospective cohort study was carried out in a 30-bed medical-surgical ICU in London to determine whether culturing throat and rectal swabs would identify more cases of methicillin-resistant Staphylococcus aureus (MRSA) colonization than just swabbing at keratinized skin carriage sites such as the anterior nares, perineum, and axillae. Swabs from all these sites were cultured routinely in all patients on admission to the ICU during a 15-month period. The authors also cultured wounds and clinical specimens obtained during the first 48 hours in the ICU.
Complete sets of culture data were obtained from 1470 out of the 1480 consecutive adult patients admitted during the study period. One-hundred and five patients (7%) had MRSA recovered on admission to the unit. Among these MRSA-colonized patients, 63 (60%) had the organism recovered on pooled keratinized skin-site swabs (anterior nares, perineum, and axillae). In 36 other patients (34%), MRSA was detected only by throat and/or rectal swabs. Throat and rectal swabs combined had a higher sensitivity (76%) than pooled keratinized skin swabs (60%; p = 0.02). Five of the 105 patients had MRSA detected only from wounds, and not from any of the other sites.
Surveillance cultures for MRSA are recommended by current international infection-control guidelines for all patients in high-risk areas, including the ICU. Using barrier protection, isolation, cohorting, and surface decolonization procedures, both transmission of colonization and the incidence of clinical nosocomial MRSA infections can be reduced. However, consensus is lacking about the best sites or combination of sites to culture in detecting MRSA colonization, with the anterior nares the most commonly used site. This study shows that culturing the anterior nares, even when specimens are combined with swabs from other keratinized areas such as the perineum and axillae, will still miss a substantial number of cases. Its findings support the addition of throat and/or rectal swabs for routine surveillance cultures, but also remind us that even when all these sites are swabbed it is also important to culture any wounds that may be present, as MRSA may be recovered only from the latter in a certain number of cases.