Does a positive Methicillin-resistant Staphylococcus aureus (MRSA) nasal swab require treatment?

Management of Positive MRSA Nasal Swabs

A positive MRSA nasal swab alone does not require treatment unless the patient has recurrent skin and soft tissue infections (SSTIs) or is at high risk for infection transmission. 1

When to Consider Decolonization

Decolonization should be considered in the following scenarios:

1. Recurrent MRSA infections: When a patient develops recurrent skin and soft tissue infections despite optimizing wound care and hygiene measures 2, 1

2. Ongoing transmission: When there is evidence of transmission among household members or close contacts despite hygiene measures 2, 1

3. Pre-operative prophylaxis: For high-risk surgeries such as orthopedic, cardiac, or neurosurgical procedures 1

Decolonization Protocol

When decolonization is indicated, the recommended approach includes:

• Nasal decolonization: Mupirocin 2% ointment applied to the anterior nares twice daily for 5-10 days 2, 1
• Body decolonization: One of the following options:
  • Chlorhexidine gluconate 2-4% body washes daily for 5-14 days 1
  • Dilute bleach baths (1 teaspoon per gallon of water or ¼ cup per ¼ tub) for 15 minutes twice weekly for up to 3 months 2, 1

Hygiene Measures

All patients with MRSA colonization should be instructed to:

• Keep draining wounds covered with clean, dry bandages 2
• Maintain good personal hygiene with regular bathing 2, 1
• Clean hands regularly with soap and water or alcohol-based hand sanitizer 2, 1
• Avoid sharing personal items like razors, towels, and linens 2, 1
• Clean high-touch surfaces (countertops, doorknobs, bathroom fixtures) with commercial cleaners 2, 1

Important Considerations

1. Screening cultures: Prior to decolonization, screening cultures are not routinely recommended if at least one prior infection was documented as MRSA 2, 1

2. Surveillance cultures: Following decolonization, surveillance cultures are not routinely recommended in the absence of active infection 2, 1

3. Mupirocin resistance: Be aware of the potential for mupirocin resistance, which has been reported with prolonged use 1, 3

4. Household contacts: Consider evaluating household contacts for evidence of S. aureus infection if there is ongoing transmission 2, 1

Clinical Utility of MRSA Nasal Swabs

Recent research has demonstrated the high negative predictive value of MRSA nasal swabs:

• 97.8% for MRSA pneumonia 4
• 97.9% for MRSA bacteremia 4
• 92.1% for MRSA wound infections 4
• 98.5% overall for any MRSA infection 4

This high negative predictive value supports using negative MRSA nasal swabs to rule out MRSA infection and guide de-escalation of empiric anti-MRSA therapy 5, 4. However, a positive nasal swab alone does not indicate active infection and should not be the sole basis for initiating treatment 6.

Common Pitfalls to Avoid

1. Overtreatment: Treating asymptomatic carriers without risk factors for infection or transmission can lead to unnecessary antibiotic use and resistance 1

2. Equating colonization with infection: A positive MRSA nasal PCR does not equate to active infection requiring treatment 6

3. Inadequate decolonization: Using mupirocin alone without addressing body colonization or environmental factors may lead to treatment failure 2, 1

4. Neglecting hygiene measures: Decolonization without concurrent hygiene measures is less likely to be successful 2, 1