The Role of Negative Methicillin-Resistant Staphylococcus aureus Nasal Surveillance Swabs in Predicting the Need for Empiric Vancomycin Therapy

BACKGROUND: The role of MRSA nasal surveillance swabs in guiding decisions about need for subsequent vancomycin therapy is unclear. Our objectives were to (1) determine the likelihood that patients with negative MRSA nasal swabs went on to develop MRSA infections during the same hospitalizations to assess if vancomycin therapy could be avoided once the nasal swab result returns negative, (2) assess days of vancomycin that potentially could be avoided, and (3) identify risk factors for having a negative MRSA nasal swab and developing an MRSA infection during the hospital stay. METHODS: This retrospective cohort study was conducted at six intensive care units (ICUs) at a tertiary care hospital in Baltimore from December 2013 to June 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 an 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. DISCLOSURES: All authors: No reported disclosures.