How do you get colonized with Methicillin-resistant Staphylococcus aureus (MRSA) or Methicillin-susceptible Staphylococcus aureus (MSSA), and how are they treated?

MRSA/MSSA Colonization: Acquisition, Treatment, and Clinical Manifestations

Decolonization with mupirocin nasal ointment 2% twice daily for 5 days with or without chlorhexidine gluconate soap is strongly recommended for MRSA and MSSA carriers, particularly before cardiac and orthopedic surgery to reduce infection risk. 1

How Colonization Occurs

Staphylococcus aureus (both MRSA and MSSA) colonization typically occurs through:

1. Person-to-person contact: Direct skin-to-skin contact with colonized individuals is the primary mode of transmission 2
2. Environmental exposure: Contact with contaminated surfaces, especially in healthcare settings 2
3. Risk factors for colonization include:
   • Healthcare exposure (hospitalization, ICU stays) 2
   • Recent antibiotic use 3
   • Male gender 3
   • Young age (less than 4 years) 3
   • Family size greater than four people 3
   • Sleeping with parents 3
   • Parental smoking 3
   • Presence of invasive devices (catheters, tubes) 4

The anterior nares are the most common colonization site, but S. aureus can also colonize the axilla, groin, perineum, and skin wounds 5.

Who Develops Symptoms vs. Who Remains Asymptomatic

Most colonized individuals (approximately 89%) remain asymptomatic carriers without developing clinical infections 4. However, certain risk factors significantly increase the likelihood of progression from colonization to infection:

Risk Factors for Developing Clinical Infection:

• Intensive care setting: 26.9 times higher risk within first four days 4
• Presence of invasive devices:
  • Intravenous catheters (4.7 times higher risk) 4
  • Surgical wounds (2.9 times higher risk) 4
  • Pressure ulcers (3.0 times higher risk) 4
• Multiple antibiotic exposure (three or more antibiotics) 4
• Immunocompromised status 1
• Presence of prosthetic material 1

Treatment Approaches

1. Decolonization for MRSA/MSSA Carriers

For pre-surgical patients:

• Strong recommendation for decolonization before cardiac and orthopedic surgery 1
• Conditional recommendation for decolonization before other types of surgery 1

Recommended decolonization regimen:

• Mupirocin nasal ointment 2% twice daily for 5 days 1
• With or without chlorhexidine gluconate soap (40 mg/mL) for bathing 1
• Timing: Complete 1-2 weeks before surgery when possible 1

For recurrent MRSA infections:

• Consider decolonization for patients with multiple recurrent MRSA skin infections despite hygiene measures 1
• Consider decolonization when there is ongoing transmission in a well-defined cohort 1

2. Treatment of Active MRSA Infections

Treatment depends on the site and severity of infection:

For bloodstream infections/bacteremia:

• Adults: Daptomycin 6 mg/kg IV once daily 6
• Alternative: Vancomycin 15-20 mg/kg IV every 8-12 hours (target trough 15-20 μg/mL) 7

For complicated skin and skin structure infections:

• Adults and pediatric patients (1-17 years): Daptomycin is indicated 6
• Duration: 7-14 days for uncomplicated infections 7

Implementation Considerations and Pitfalls

Monitoring for Resistance

• Regularly monitor for mupirocin resistance in colonizing isolates and those causing infection 1
• High prevalence of mupirocin resistance has been reported in some community settings 1

Effectiveness of Decolonization

• Decolonization with mupirocin plus chlorhexidine has shown a 30% reduction in MRSA infection risk compared to education alone 8
• Adherence to the full decolonization regimen is critical - full adherence results in 44% fewer MRSA infections 8

Limitations and Cautions

• Decolonization has limited effectiveness in patients colonized at multiple body sites 5
• The optimal regimen, frequency, and duration for non-surgical patients remains unclear 1
• Side effects of decolonization regimens are generally mild and occur in approximately 4.2% of patients 8

Algorithm for Management

1. Screen high-risk patients for MRSA/MSSA colonization, especially before high-risk surgeries
2. For colonized patients:
   • If scheduled for cardiac/orthopedic surgery: Implement decolonization with mupirocin ± chlorhexidine
   • If scheduled for other surgeries: Consider decolonization based on individual risk factors
   • If experiencing recurrent infections: Implement decolonization plus personal/environmental hygiene measures
3. For active infections: Treat with appropriate antibiotics based on site and severity
4. For prevention of recurrence:
   • Cover infected skin and draining wounds
   • Avoid sharing personal items
   • Use commercial cleaners for high-touch surfaces
   • Consider regular decolonization for those with recurrent infections

By following this evidence-based approach, clinicians can effectively manage MRSA/MSSA colonization and reduce the risk of subsequent infections, particularly in high-risk populations.