What is the recommended workup for MRSA?

Recommended Workup for MRSA

The recommended workup for MRSA should include nasal swab screening using PCR-based methods as the primary diagnostic approach, combined with appropriate clinical cultures from suspected infection sites. 1, 2

Screening Approach

Who Should Be Screened

• Screen patients at high risk for MRSA carriage, including those with:
  • Prior hospitalization 3
  • History of previous MRSA infection 3
  • Admission to intensive care units 2
  • Contact with known MRSA carriers 3
  • Skin ulcers or wounds 3

When to Screen

• Perform screening at admission for high-risk patients 3
• Consider periodic screening during hospitalization for patients with ongoing risk factors 3
• Repeat screening may be necessary if initial results are negative but clinical suspicion remains high 3

How to Screen

Specimen Collection

• Nasal swabs are the primary screening method, but have limited sensitivity (approximately 66-70%) when used alone 4, 5
• For improved detection, consider combining nasal swabs with other sites:
  • Nasal plus perineal swabs provide the best two-site combination (82% sensitivity) 4
  • For higher sensitivity, include throat swabs along with nasal specimens 3
  • Always culture clinically relevant sites (wounds, invasive devices) 4

Collection Technique

• Use flocked swabs or foam-tipped swabs for optimal bacterial recovery 6
• Swab both anterior nares thoroughly 3
• Place swabs in appropriate transport medium (Amies medium provides better preservation) 6

Laboratory Methods

• PCR-based detection methods provide:
  • Higher sensitivity (88% vs 65.5% for chromogenic media) 2
  • Faster turnaround time (approximately 1.5 hours) 1
  • Better negative predictive value (96.5%) 5
• Alternative methods include:
  • Direct plating on selective chromogenic media 3
  • Enrichment broth culture methods 1

Clinical Cultures

When to Obtain Clinical Cultures

• Always obtain cultures from:
  • Purulent drainage or exudate 3
  • Abscesses requiring incision and drainage 3
  • Suspected infection sites in patients with systemic signs of infection 3
  • Wounds with signs of infection 3

Interpretation of Results

• Positive nasal screening has moderate positive predictive value (82.5%) 1
• Negative nasal screening has high negative predictive value (96.5-99.2% depending on infection site) 5
• Negative MRSA nasal screening may be used to guide de-escalation of empiric anti-MRSA therapy 5

Management Considerations

Infection Control Measures

• Implement contact precautions for colonized individuals 3
• Consider decolonization for:
  • Patients with recurrent MRSA skin and soft tissue infections 3
  • Situations with ongoing transmission among household members 3
• Decolonization regimens include:
  • Nasal mupirocin ointment twice daily for 5-10 days 3, 7
  • Chlorhexidine body washes or dilute bleach baths 3

Environmental Measures

• Focus cleaning on high-touch surfaces 3
• Use appropriate cleaners according to label instructions 3
• Avoid sharing personal items (towels, razors) 3

Common Pitfalls and Caveats

• Nasal screening alone misses approximately 30-35% of MRSA carriers 4, 5
• Screening sensitivity decreases significantly when performed more than 6 days before clinical cultures (79% vs 46%) 2
• Different swab types yield significantly different recovery rates - flocked or foam-tipped swabs perform better than rayon swabs 6
• Community-acquired MRSA strains may have different colonization patterns than healthcare-associated strains 3
• Screening results should be interpreted in the context of local MRSA prevalence and patient risk factors 3