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Multiple Site Testing for MRSA Carriage Increases Detection by 25%

Screening multiple anatomic sites for methicillin-resistant Staphylococcus aureus (MRSA) increased detection of the bacteria by 25% compared with single site testing of the anterior nares alone.

Investigators from the University of Wisconsin-Madison presented data at ASM Microbe 2019 evaluating the necessity of multiple site testing (MST) for MRSA.

“Identification of MRSA carriage helps reduce transmission and guide antimicrobial therapy. Molecular testing via polymerase chain reaction (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 2000s at high MRSA prevalence centers,” investigators wrote. “In this study, we sought to determine the ability of MST to increase MRSA detection at a low prevalence academic center.”

A total of 4484 patients were enrolled in the study, 549 (12%) of whom were <18 years old and 3935 (88%) of whom were ≥18 years old. Investigators performed MRSA PCR with an overall positivity rate for all anatomic sites at 313/4480 (7%). The research team used single site testing (SST) for 1442 (32%) patients with 54 positive (4%) results. MST was performed on 3037 (68%) patients and 255 (8%) were positive from at least 1 site tested.

“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),” investigators determined.

Overall, the use of MST increased MRSA detection by 25%, and positive results are more likely to be discordant than concordant across different anatomic sites, the research team wrote.

“This [research] highlights the importance of using MST at low prevalence centers, when clinically indicated (eg, ruling out MRSA pneumonia, preoperative screening),” investigators concluded.

The poster, “Necessity of Screening Multiple Anatomic Sites for Methicillin-Resistant Staphylococcus aureus (MRSA) Carriage,” was presented Friday, June 21, 2019, at ASM Microbe 2019 in San Francisco, California.
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