What are the risk factors for Methicillin-resistant Staphylococcus aureus (MRSA) infections?

Risk Factors for MRSA Infections

Prior MRSA infection or colonization is the single strongest risk factor for developing MRSA infection, followed by recent hospitalization, nursing home residence, and recent antibiotic use. 1

Major Risk Factors for MRSA Infection

Healthcare-Associated Risk Factors

• Prior MRSA infection or colonization (strongest predictor) 2, 1
• Recent hospitalization 1
• Nursing home residence 1
• Recent antibiotic therapy, especially prolonged or inappropriate use 2, 1, 3
• Prolonged hospital stay 1, 3
• Presence of invasive devices:
  • Central venous catheters 1, 3
  • Intravascular catheters 1
  • Dialysis catheters 1
  • Tracheostomies 4
  • Nasogastric tubes 4
• ICU admission 3
• Surgical procedures 3
• Total parenteral nutrition 3

Patient-Specific Risk Factors

• Advanced age 1, 4
• Nasal colonization with MRSA (20-40% of general population) 2, 1
• Chronic comorbidities:
  • Diabetes mellitus 2, 1
  • Chronic obstructive pulmonary disease (COPD) 1
  • Immunosuppression 1
  • Severe underlying disease 4
  • Charlson score >5 points 1
• Skin wounds or conditions:
  • Cellulitis 5
  • Skin ulcers 5
  • Chronic skin lesions 1

Community-Associated Risk Factors

• Close contact with MRSA-colonized individuals 1
• Living in crowded conditions 1
• Participation in contact sports 1
• Sharing personal items 1
• Injection drug use 1
• Men who have sex with men 1
• Children <2 years old 1

Environmental Risk Factors

• Presence of multiple MRSA-colonized patients in the same unit 3, 6
• Environmental contamination 6
• High local prevalence of MRSA (>30-50% of S. aureus isolates) 2

Clinical Presentation Risk Factors

• Post-influenza-like illness 2, 1
• Concurrent skin and soft tissue infection 1
• Septic shock 1
• Severe infection requiring ICU admission 1

Important Clinical Considerations

Identifying High-Risk Patients

When evaluating patients for potential MRSA infection, prioritize screening those with:

1. Previous MRSA history (highest risk factor) 1
2. Recent healthcare exposure with antibiotic use 1, 3
3. Presence of indwelling devices, especially central venous catheters 3
4. Severe underlying disease with prolonged hospitalization 4

Community vs. Healthcare-Associated MRSA

The distinction between healthcare-associated and community-acquired MRSA has become increasingly blurred 2. However:

• Healthcare-associated MRSA typically affects patients with the risk factors listed above
• Community-acquired MRSA often causes skin and soft tissue infections in otherwise healthy individuals, particularly children and young adults 7

Empiric Treatment Considerations

Empiric MRSA coverage should be considered when:

• Patient has history of previous MRSA infection/colonization within the past year 2
• Local MRSA prevalence is high (approximately 50% for mild infections, 30% for moderate infections) 2
• Infection is severe enough that failure to cover MRSA poses significant risk 2

Prevention Strategies

• Appropriate hand and skin hygiene 1
• Cleaning and disinfecting shared equipment 1
• Prompt treatment of skin wounds 1
• Mupirocin nasal ointment for carriers (reduces recurrences by ~50%) 1
• Oral clindamycin for recurrent furunculosis (reduces subsequent infections by ~80%) 1
• Active surveillance in high-risk settings 6

Understanding these risk factors is essential for early identification, appropriate treatment, and prevention of MRSA infections, which can significantly reduce morbidity and mortality associated with these infections.