107 A Negative Nares Screen in Combination with Absence of Clinical Risk Factors Can be Used to Identify Patients with Very Low Likelihood of Methicillin-resistant Staphylococcus Aureus Infection in a Veterans Affairs Hospital

Friday, March 19, 2010
Grand Hall (Hyatt Regency Atlanta)
Sadao Jinno, MD , University Hospitals of Cleveland Case Medical Center, Cleveland, OH
Shelley Chang, PhD , Case Western Reserve University, Cleveland, OH
Curtis Donskey , Louis Stokes Cleveland VA Medical Center, Cleveland, OH
Background:   Hospitalized patients with suspected infectious syndromes often receive empiric treatment with vancomycin to cover for methicillin-resistant Staphylococcus aureus (MRSA). Screening for nares carriage of MRSA could be used to identify patients at low risk for MRSA infection who do not require empiric vancomycin. However, it has been demonstrated that a significant proportion of patients with MRSA infection may have negative concurrent nares screening results.  
Objective: To test the hypothesis that a negative nares screen in combination with absence of other clinical risk factors for MRSA can be used to predict a low likelihood of MRSA infection in patients receiving empiric vancomycin. 
Methods: A 5-month prospective cohort study was performed at a Veterans Affairs hospital to test the ability of nares MRSA PCR screen results alone or in combination with clinical factors from 4 different prediction rules to identify patients at low risk for MRSA infection. The prediction rules for MRSA infection were derived from a prior case-control study from our institution (Model 1), presenting clinical syndrome (Model 2), a combination of published risk factors for MRSA infection (Model 3), and previous prediction rules developed to detect MRSA carriage (Model 4). All inpatients receiving empiric vancomycin for undiagnosed infectious diseases syndromes were included.
Results: Of 347 patients receiving empiric vancomycin for suspected MRSA infection, 43 (12%) had confirmed MRSA infection. Only 61% of patients with MRSA infection had positive nares PCR results within the previous 2 weeks, and a negative nares screen was not reliable to predict a low risk of infection (NPV 94%). Of the 4 models tested, Model 1 (Combination of nares screening test and/or suspected line infection/suspected sepsis, immunosuppressive agents, homeless or long-term care facility resident, skin and soft tissue infection, history of incarceration, spinal cord injury, previous MRSA infection, and both diabetes mellitus (DM) and end-stage renal disease and Model 3 (Having any of variables included in model 1 but excluding DM, suspected healthcare-associated pneumonia/ septic arthritis, and intravenous drug use) were 100% sensitive and both accurately excluded those at low risk for MRSA infection (100% NPV). The application of these prediction rules could potentially reduce empiric vancomycin prescriptions in our institution by up to 28%.
Conclusions: In the inpatient VA population, a negative nasal screen in combination with absence of certain clinical risk factors could be used to predict patients with a very low likelihood of MRSA infection. Application of prediction rules could significantly reduce empirical vancomycin prescriptions without missing any patients with MRSA infection.