Bloodstream infections with Staphylococcus aureus are clinically significant and 
are often treated with empirical methicillin resistance (MRSA, 
methicillin-resistant S. aureus) coverage. However, vancomycin has associated 
harms. We hypothesized that MRSA screening correlated with resistance in S. 
aureus bacteremia and could help determine the requirement for empirical 
vancomycin therapy. We reviewed consecutive S. aureus bacteremias over a 5-year 
period at two tertiary care hospitals. MRSA colonization was evaluated in three 
ways: as tested within 30 days of bacteremia (30-day criterion), as tested 
within 30 days but accounting for any prior positive results (ever-positive 
criterion), or as tested in known-positive patients, with patients with unknown 
MRSA status being labeled negative (known-positive criterion). There were 409 S. 
aureus bacteremias: 302 (73.8%) methicillin-susceptible S. aureus (MSSA) and 107 
(26.2%) MRSA bacteremias. In the 167 patients with MSSA bacteremias, 7.2% had a 
positive MRSA test within 30 days. Of 107 patients with MRSA bacteremia, 68 were 
tested within 30 days (54 positive; 79.8%), and another 21 (19.6%) were 
previously positive. The 30-day criterion provided negative predictive values 
(NPV) exceeding 90% and 95% if the prevalence of MRSA in S. aureus bacteremia 
was less than 33.4% and 19.2%, respectively. The same NPVs were predicted at 
MRSA proportions below 39.7% and 23.8%, respectively, for the ever-positive 
criterion and 34.4% and 19.9%, respectively, for the known-positive criterion. 
In MRSA-colonized patients, positive predictive values exceeded 50% at low 
prevalence. MRSA screening could help avoid empirical vancomycin therapy and its 
complications in stable patients and settings with low-to-moderate proportions 
of MRSA bacteremia.