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

Risk Factors for MRSA Infection

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

Healthcare-Associated Risk Factors

Healthcare exposure remains the predominant risk pathway for MRSA acquisition:

• Prior MRSA infection or colonization within the past year 1, 2
• Recent hospitalization (within previous 1-24 months) 1, 3
• Nursing home or long-term care facility residence 1, 3, 4
• Recent antibiotic exposure (particularly beta-lactams, fluoroquinolones, or macrolides within past 3 months) 1, 3
• Prolonged hospital stay (current duration >16 days) 1
• Presence of invasive devices at time of admission:
  • Indwelling urinary catheters 3
  • Central venous catheters 1
  • Endotracheal tubes 5
  • Nasogastric tubes 5
  • Surgical drains 5
• Recent surgery or surgical wounds 5
• Dialysis 1, 2
• Recent outpatient healthcare visits 6

Patient-Specific Risk Factors

Several patient characteristics increase MRSA risk:

• Advanced age (≥75 years) 1
• Chronic comorbidities:
  • Diabetes mellitus 1
  • Chronic obstructive pulmonary disease 1
  • Immunosuppression 1, 2
  • HIV infection 1, 2
• Pressure ulcers or chronic wounds 5
• Charlson score >5 points 1

Community-Associated Risk Factors

Community-associated MRSA (CA-MRSA) has distinct risk factors:

• Close contact with MRSA-colonized individuals 1, 6
• Living in crowded conditions:
  • Military barracks 6
  • Correctional facilities 1, 2
  • Homeless shelters 4
• Participation in contact sports 1, 2
• Injection drug use 1, 2, 6
• Men who have sex with men 1, 2
• Children <2 years old 1, 2

Clinical Risk Factors

Certain clinical presentations increase MRSA risk:

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

Geographic Considerations

• Local MRSA prevalence is important - empiric MRSA coverage is recommended when local prevalence exceeds 20% of S. aureus isolates 1, 2
• Residence in areas with high MRSA circulation 1

Common Pitfalls in MRSA Risk Assessment

1. Failure to recognize healthcare-associated MRSA in outpatients: Many "community" MRSA cases actually have healthcare risk factors.

2. Overlooking prior colonization: Previous MRSA colonization is one of the strongest predictors of subsequent infection.

3. Underestimating the importance of local epidemiology: Local prevalence rates should guide empiric therapy decisions.

4. Neglecting device-related risks: Invasive devices significantly increase MRSA risk and should prompt consideration of empiric MRSA coverage.

5. Assuming all MRSA strains are healthcare-associated: CA-MRSA strains have distinct epidemiology and often affect otherwise healthy individuals without traditional healthcare risk factors.

Understanding these risk factors allows for appropriate infection control measures, targeted surveillance, and judicious use of anti-MRSA antibiotics to both treat infections effectively and practice good antimicrobial stewardship.