What’s in your toolbox? MRSA Screening

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Lauren Igneri
Critical care pharmacist and proud Rutgers University graduate. Enjoys rock climbing, cycling, travel, and lively discussions on the finer points of pharmacokinetics and critical care over a beer with friends.

The Pre-brief

  • From 2011-2014, Staphylococcus aureus was the second-most prevalent pathogen for all hospital-acquired infections.
    • Most common organism implicated in ventilator-associated pneumonia (VAP) or surgical site infections (SSI).
    • The common pathogen in community-acquired skin and soft tissue infections (SSTIs).
  • Methicillin-resistant S. aureus (MRSA) isolates in VAP, SSI, central line-associated bloodstream infections (CLABSI), or catheter-associated urinary tract infections (CAUTIs) have been reported to range from 42.4-55.8%. Therefore, anti-MRSA therapy (e.g. vancomycin) is the cornerstone of empirical antimicrobial regimens.
  • S. aureus commonly colonizes the nares, throat, axillae, rectum, and groin.
    • Surveillance nares screening for MRSA has historically been utilized for infection control measures. 
  • The absence of MRSA nares colonization has been shown to be a negative predictor of MRSA pulmonary infections.
    • Recent literature has highlighted MRSA nasal screening as a useful test to minimize unnecessary empiric anti-MRSA therapy.

Overall, MRSA nares screening has a high specificity and NPV for ruling out MRSA pneumonia. Most studies included in the meta-analysis by Parente et al. utilized protocols to screen for MRSA in the nares at ICU admission, with some repeating the screening weekly. However, the study by Mallidi et al. demonstrated the NPV remained high (98%) even when using nares screens from within 60 days of hospital admission, indicating MRSA nares screening from a recent hospital admission may successfully guide empiric antimicrobial therapy in the ED and ICU settings. 

Reducing vancomycin overuse is a major focus of hospital AMS programs. One study demonstrated a mean reduction in duration of vancomycin therapy from 74 hours to 27.4 hours (p<0.0001) and number of patients requiring vancomycin therapeutic drug monitoring from 48.1% to 16.7% following implementation of a pharmacist-driven protocol to order MRSA screening in patients with CAP, HCAP, or HAP.  Appropriate interpretation of MRSA nasal screens and patient follow-up is needed to ensure success with using results for antimicrobial de-escalation. MRSA nasal screen results should be interpreted cautiously in the setting of recent decolonization.

The Debrief

  • MRSA nares screening is a valuable tool for antimicrobial stewardship (AMS) initiatives to streamline empiric antibiotic therapy in patients with pneumonia.
    • High specificity and NPV for ruling out MRSA pneumonia 
    • Significantly reduces the duration of empiric anti-MRSA therapy
  • Appropriate interpretation of MRSA nasal screens and continuous patient follow-up is needed for antimicrobial de-escalation strategies.

References:

  1. Mergenhagen KA, Starr KE, Wattengel BA, et al. Determining the Utility of Methicillin-Resistant Staphylococcus aureus Nares Screening in Antimicrobial Stewardship. Clin Infect Dis. 2020; 71:1142-1148.
  2. Carr AL, Daley MJ, Givens Merkel K, Rose DT. Clinical Utility of Methicillin-Resistant Staphylococcus aureus Nasal Screening for Antimicrobial Stewardship: A Review of Current Literature. Pharmacotherapy. 2018; 38:1216-1228.
  3. Parente DM, Cunha CB, Mylonakis E, Timbrook TT. The Clinical Utility of Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Screening to Rule Out MRSA Pneumonia: A Diagnostic Meta-analysis With Antimicrobial Stewardship Implications. Clin Infect Dis. 2018; 67:1-7.
  4. Mallidi MG, Slocum GW, Peksa GD, DeMott JM. Impact of Prior-to-Admission Methicillin-Resistant Staphylococcus aureus Nares Screening in Critically Ill Adults With Pneumonia. Ann Pharmacother. 2021; Jun 6:10600280211023209. Epub ahead of print.
  5. Baby N, Faust AC, Smith T, et al. Nasal methicillin-resistant Staphylococcus aureus (MRSA) PCR testing reduces the duration of MRSA-targeted therapy in patients with suspected MRSA pneumonia. Antimicrob Agents Chemother. 2017; 61(4):e02432-16.

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