771. Modified Two Culture Rule in the Identification of Veterans Persistently Colonized with MRSA and Risk of Subsequent Infection in Atlanta and Denver
Session: Oral Abstract Session: Staph aureus: Screening and Prevention
Friday, October 21, 2011: 2:45 PM
Room: 157ABC
Background: Persistent nasal carriers have an increased risk of subsequent MRSA infection. Previous work has shown two nasal cultures one week apart adequately predicts persistent colonization with MRSA. This study evaluates a simple method of determining the carriage state of veterans and provides additional insight to the risk of subsequent MRSA infection. Methods: Since Oct 07, all hospitalized veterans at 2 VA facilities (Atlanta and Denver) were screened for MRSA colonization on admission, transfer, and discharge. All colonization data was extracted from the electronic medical record from Oct 07 to Dec 10. To determine if two consecutive positive swab results predict the persistent carriage state, we identified a group of veterans in which colonization status was known (those with 5 or more nasal swabs in the medical record) and evaluated their first two swab results. As used in other studies, >= 80% of swabs positive represent true persistent colonization. Sensitivity and specificity were calculated. All clinical MRSA cultures were reviewed monthly and categorized based on standard NHSN definitions. Infection free survival was determined based on colonization status. Results: In the subgroup of patients with known colonization status (5 or more swabs), the modified two culture rule had a sensitivity of 81% and specificity of 97%. Applying this rule to all patients in Atlanta identified 633 persistently colonized patients (first two swabs both positive) and 9225 non-persistently colonized patients (first two swabs not both positive). In Denver, 440 patients were persistently colonized and 9069 were non-persistently colonized. Atlanta veterans are more likely to be persistently colonized (p < 0.0001). Subsequent MRSA infection occurred in 139 (13.0%) persistently colonized patients and 335 (1.8%) non-persistently colonized patients. The infection free survival times were significantly different over the course of the study (log rank: p < 0.0001). Conclusion: Using two consecutive MRSA nasal screening swab results adequately identified patients persistently colonized with MRSA. The risk of developing subsequent MRSA infection in persistently colonized patients is approximately 7 times the risk of those non-persistently colonized.

Subject Category: C. Clinical studies of bacterial infections and antibacterials including sexually transmitted diseases and mycobacterial infections (surveys, epidemiology, and clinical trials)

Edward Stenehjem, MD1,2, David Rimland, MD1,2 and Mary Bessesen, MD3, (1)Atlanta VA Medical Center, Decatur, GA, (2)Emory University School of Medicine, Decatur, GA, (3)VA Eastern Colorado Health Care System and University of Colorado School of Medicine, Denver, CO


E. Stenehjem, None

D. Rimland, None

M. Bessesen, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.