Determining the utility of methicillin-resistant Staphylococcus aureus nares screening in antimicrobial stewardship

Kari A Mergenhagen, Kaitlyn E Starr, Bethany A Wattengel, Alan J Lesse, Zarchi Sumon, John A Sellick
Clinical Infectious Diseases: An Official Publication of the Infectious Diseases Society of America 2019 October 1

BACKGROUND: Treatment of suspected methicillin-resistant Staphylococcus aureus (MRSA) is a cornerstone of many antibiotic regimens; however, antibiotics are associated with toxicity. The Department of Veterans Affairs (VA) hospitals screen each patient on admission and transfer for MRSA nares colonization. The objective of this study was to determine the negative predictive value (NPV) of MRSA screening in the determinization of subsequent positive clinical culture for MRSA. High NPVs with MRSA nares screening maybe used as a stewardship tool for de-escalation as well as avoidance of anti-MRSA therapy.

METHODS: This was a retrospective cohort study across VA medical centers nationwide from January 1, 2007 to January 1, 2018. Data from patients with MRSA nares screening upon admission or transfer were obtained from the VA Corporate Data Warehouse. Subsequent clinical cultures within 7 days of the nares swab were evaluated for presence of MRSA. Sensitivity, specificity, positive predictive values (PPVs), and NPVs were calculated for the entire cohort, as well as subgroups for specific culture sites.

RESULTS: This cohort yielded 561,325 clinical cultures from a variety of anatomical sites. The sensitivity and specificity for positive MRSA clinical culture were 67.4% and 81.2%, respectively. The NPV of MRSA nares screening for ruling out MRSA infection was 96.5%. The NPV for bloodstream infections was 96.5%, for intra-abdominal cultures was 98.6%, for respiratory cultures was 96.1%, for wound cultures was 93.1%, and for cultures from the urinary system was 99.2%.

CONCLUSION: Given the high NPVs, MRSA nares screening may be a powerful stewardship tool for de-escalation and avoidance of empirical anti-MRSA therapy.

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