TIL: MRSA nares swab has an almost perfect NPV
The MRSA nares swab is very poor at predicting whether someone could have MRSA, but it has an EXTREMELY high negative predictive value (NPV)
In 2014, a study1 came out saying that for patients with Pneumonia, the NPV was 99.2%. Multiple other studies confirmed this for PNEUMONIA specifically. Meaning, if it was negative, your pneumonia was likely not from MRSA. But what about other infections, you might ask
In 2019, a study done across VA systems nationwide2 showed that with other types of infection, the NPV was still really high!
-Pneumonia (96.5)
-Wound infection (93%)
-Intr-ab (98.6)
-Urinary (99%)
-And overall, Washington state (where I was at the time of this post) had one of the HIGHEST NPVs (all states on avg were above 93%)
But this study had limitations: these are all vets, barely any women, VA antibiograms are not the same as many other community hospitals
1. Dangerfield, Benjamin et al. “Predictive value of methicillin-resistant Staphylococcus aureus (MRSA) nasal swab PCR assay for MRSA pneumonia.” Antimicrobial agents and chemotherapy vol. 58,2 (2014): 859-64. doi:10.1128/AAC.01805-13
2. Mergenhagen, Kari et al. "Determining the Utility of Methicillin-Resistant Staphylococcus aureus Nares Screening in Antimicrobial Stewardship." Clinical Infectious Diseases, Volume 71, Issue 5, 1 September 2020, Pages 1142–1148, https://doi.org/10.1093/cid/ciz974
