Methods: This retrospective cohort study was conducted at 6 intensive care units (ICUs) at a tertiary care hospital in Baltimore from 12/2013-6/2015. MRSA nasal swabs are obtained at the time of admission and weekly thereafter for all ICU patients. The negative predictive value (NPV), defined as the ability of a negative MRSA nasal screening test to correctly predict no subsequent MRSA infection during the hospital stay, was calculated, accounting for the 3-day turnaround time of MRSA nasal surveillance swabs. Days of vancomycin therapy started or continued after 3 days from the first negative MRSA nasal swab were determined by chart review. A matched case-control study was performed to identify risk factors for patients with negative MRSA surveillance cultures who subsequently developed MRSA infections.
Results: Of 11,441 MRSA-nasal swab negative patients, the proportion of subsequent incident MRSA infections was 0.2%. Negative MRSA surveillance swabs had a NPV of 99.4% (95% CI 99.1-99.6%). Among 4,091 MRSA-negative patients receiving vancomycin, vancomycin was started or continued after 3 days since the first MRSA-negative nasal swab in 1,434 patients (35%), translating to 7,377 potentially avoidable vancomycin days. The matched case-control analysis did not identify risk factors associated with subsequent MRSA infection.
Conclusion: At our institution with robust infection control practices and low nosocomial MRSA transmission rates, patients with negative MRSA nasal swabs have a very low likelihood of subsequent MRSA infection during hospitalizations. MRSA nasal swabs can provide useful information when determining whether to initiate or stop empiric vancomycin.
A. Gadala, None
S. E. Cosgrove, None