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FRIDAY - CPHM-906 - Necessity of Screening Multiple Anatomic Sites for Methicillin-Resistant Staphylococcus aureus (MRSA) Carriage

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Author Block: T. Choera, A. Lepak, D. J. Chen; Univ. of Wisconsin-Madison, Madison, WI
Disclosure Block: T. Choera: None. A. Lepak: None. D.J. Chen: None.
Background: Identification of MRSA carriage helps reduce transmission and guide antimicrobial therapy. Molecular testing (PCR) of swabs from the anterior nares (AN) is commonly performed to rapidly detect MRSA; however, testing additional anatomic sites, such as the oropharynx (OP) and/or axilla and groin (AG), has been reported to increase sensitivity in studies from the early 2000’s at high MRSA prevalence centers. In this study, we sought to determine the ability of multiple site testing (MST) to increase MRSA detection at a low prevalence academic center. Methods: MRSA PCR tests were performed using Xpert SA Nasal Complete (Cepheid; FDA-cleared and modified). Results were retrieved from 1/2017-7/2018, including both inpatient and outpatient settings, and analyzed based on patient age (<18yo or ≥18yo) and anatomic site(s) tested (AN, OP, and/or AG). Specimens collected from the same patient on different calendar days were counted as independent events. Results: MRSA PCR tests were performed on 4484 patients; 549 (12%) were <18yo and 3935 (88%) were ≥18yo. Four invalid PCR results were excluded from subsequent analyses. The overall MRSA PCR positivity rate for all anatomic sites tested was relatively low at 313/4480 (7%). Single site testing (SST) was performed on 1443 (32%) patients with 54 positive (4%) results. Positivity rates for SST for those <18yo were: 6/426 (1%) AN, 0/1 (0%) OP, and 1/7 (14%) AG. For those ≥18yo, SST positivity rates were: 39/832 (5%) AN, 1/42 (2%) OP, and 7/135 (5%) AG. MST was performed on 3037 (68%) patients and 255 (8%) were positive from at least one site tested. Distribution of MRSA PCR results for MST is shown (see Table). For those with a positive MRSA result from MST, AN was positive in 202/253 (80%) cases where AN sampling was included, OP in 88/121 (73%), and AG in 89/155 (57%); anatomic sites were more commonly discordant for MRSA detection (n=139) than they were concordant (n=116) Conclusion: MST, compared to SST of AN alone, increases MRSA detection by 25%. When results are positive, they are more likely to be discordant than concordant across different anatomic sites. This highlights the importance of using MST at low prevalence centers, when clinically indicated (e.g. ruling out MRSA pneumonia, preoperative screening).
Multiple Site MRSA PCR ResultsFrequency
ANOPAG<18yo≥18yoTotal
++05959
+02525
+02020
1012391249
++44650
+55560
+12728
9313691462
++011
+011
044
+++156
++011
+011
++011
+011
+101
06767
11529223037