368: METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS SCREENING RESULTS AS A GUIDE FOR EMPIRIC ANTIBIOTIC SELECTION IN MEDICAL INTENSIVE CARE UNIT PATIENTS

Abstract

Various surveillance programs have been implemented in medical intensive care units (MICUs) to detect patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) for isolation purposes, but whether this testing can be used to guide empiric antimicrobial therapy is controversial.

The objectives were to determine if screening results for nasal colonization of MRSA are predictive of the development of any infection and if an infection occurs, whether the screening accurately predicts the need for empiric MRSA coverage.

A retrospective chart review of patients admitted to the MICU of St. Vincent between January 1st and June 31st 2011 was conducted. A total of 417 adult patients with admission MRSA nasal swabs and who were hospitalized in the MICU for >72 hours were included. A clinically significant infection was defined as either a positive blood culture with Staphylococcus sp., Streptococcus sp., a gram-negative sp., or other non-contaminant bacteria or a positive non-blood culture and treatment with appropriate antibiotics for >48 hours following the culture collection. Data collected was analyzed for sensitivity, specificity, positive and negative predictive values (PPV/NPV), and positive and negative likelihood ratios (PLR/NLR).

There was no clinically significant difference in the development of any infection between patients with a positive nasal swab (PNS) or a negative nasal swab (NNS) at admission. However, 5.6% of patients with infections who were admitted with a NNS developed a MRSA infection compared to 43.8% of patients who had a PNS (p=0.0002). The test results ability to predict MRSA compared to another organism as the source of an infection demonstrated a specificity of 91.8%, NPV of 94.4%, PLR of 6.56 and NLR of 0.5.

Our study demonstrated MRSA screening results do not accurately predict a patient’s risk of developing an infection from any organism, but patients who do develop an infection in the MICU with positive nasal swab results would benefit from empiric MRSA coverage while those with negative screening results may not.