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

Risk Factors for Methicillin-Resistant Staphylococcus aureus (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, especially in patients with chronic comorbidities. 1

Major Risk Factors for MRSA Infection

Healthcare-Associated Risk Factors

• Prior MRSA infection or colonization (strongest predictor) 1
• Recent hospitalization or healthcare exposure 1, 2
• Nursing home residence 1, 2
• Recent antibiotic use, especially multiple antibiotics 1, 3
• Prolonged hospital stay 1, 3
• Presence of invasive devices:
  • Central venous catheters 1, 3
  • Urinary catheters 4
  • Endotracheal tubes 4
  • Nasogastric tubes 4
  • Surgical drains 4
• Dialysis/hemodialysis 1
• ICU admission (particularly surgical ICUs) 3

Patient-Specific Risk Factors

• Advanced age 1
• Chronic comorbidities:
  • Diabetes mellitus 1
  • Chronic obstructive pulmonary disease (COPD) 1
  • Congestive heart failure 2
  • Renal failure 2
  • Immunosuppression 2
• Charlson score >5 points 1
• Presence of wounds:
  • Surgical wounds 5, 4
  • Pressure ulcers 4
• Nasal MRSA colonization (occurs in 20-40% of the general population) 1, 3
• Post-influenza-like illness 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
• High local prevalence of MRSA (>30-50% of S. aureus isolates) 1

Environmental Risk Factors

• Presence of multiple MRSA-colonized patients in the same unit 3
• High local prevalence of MRSA 1

Clinical Implications

When evaluating patients for potential MRSA infection, the Infectious Diseases Society of America (IDSA) recommends considering empiric MRSA coverage in patients with:

• History of previous MRSA infection/colonization within the past year 5, 1
• High local MRSA prevalence 1
• Severe infection 1
• Risk factors for MRSA such as nasal colonization, prior MRSA infection, recent hospitalization, or recent antibiotic use 5

For surgical site infections specifically, IDSA guidelines recommend considering MRSA coverage when risk factors are present, including systemic signs of infection with erythema/induration extending >5 cm from the wound edge, temperature >38.5°C, heart rate >110 beats/minute, or WBC count >12,000/µL 5.

Prevention Strategies

• Active surveillance in high-risk settings 1
• Appropriate hand and skin hygiene 1
• Cleaning and disinfecting shared equipment 1
• Prompt treatment of skin wounds 1
• For recurrent infections:
  • Mupirocin nasal ointment (reduces recurrences by ~50%) 1
  • Oral clindamycin 150 mg daily for 3 months (reduces subsequent infections by ~80% for recurrent furunculosis) 1

Understanding these risk factors is crucial for implementing appropriate preventive measures and initiating timely empiric therapy when MRSA infection is suspected.