“If your patient has a negative MRSA nasal swab, and you are using vancomycin to empirically cover hospital-associated pneumonia, you can stop the vanc.”
Yes!!! It turns out this is true. There was a study in 2014 from Arizona that looked at how MRSA nasal swab results correlated with MRSA pneumonia: “The MRSA PCR assay demonstrated 88.0% sensitivity and 90.1% specificity, with a positive predictive value of 35.4% and a negative predictive value of 99.2%.” This means that although a positive MRSA swab doesn’t mean your patient will get MRSA pneumonia, if they are negative for MRSA, there is an excellent chance that they will not have MRSA pneumonia and so empiric vancomycin is not indicated unless there are extenuating circumstances. This was also seen in an earlier study.
What about stopping vancomycin for empiric treatment of other infections, like cellulitis? That is more contentious. There is evidence to suggest that very few cases of MRSA infection would be missed if MRSA-negative patients did not receive vancomycin, but many would argue that it is more important to treat any possible MRSA infection.
Interesting aside: another study looking at rates of MRSA disease found that patients can still develop MRSA infections even if their nasal swab is negative though: “nearly a third of MRSA-infected patients were not nasally colonized, suggesting that nasal colonization need not precede disease and that a negative test for nasal colonization would not rule out MRSA disease in settings of moderate or high prevalence.”