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

Risk Factors for Methicillin-resistant Staphylococcus aureus (MRSA)

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

Patient-Related Risk Factors

Previous MRSA History and Colonization

• Prior MRSA infection or colonization (strongest predictor) 1
• Nasal colonization with MRSA (occurs in 20-40% of general population) 1
• History of MRSA-positive clinical culture from a superficial body site in the preceding 12 months (23-fold increased risk) 2

Demographic and Health Status

• Advanced age 1
• Male sex (2.9-fold increased risk) 2
• Chronic comorbidities:
  • Diabetes mellitus
  • Chronic obstructive pulmonary disease (COPD)
  • Immunosuppression
  • High Charlson comorbidity score (>5 points) 1

Skin and Wound-Related Factors

• Presence of pressure ulcers (3-fold increased risk) 3
• Surgical wounds (2.9-fold increased risk) 3
• Skin trauma or breaks in skin integrity 1

Healthcare-Related Risk Factors

Healthcare Exposure

• Recent hospitalization (especially with length of stay >5 days) 1, 2
• Nursing home residence 1
• Recent antibiotic use (particularly broad-spectrum antibiotics) 1
• Administration of three or more antibiotics 3
• Hemodialysis (21-fold increased risk) 2

Invasive Devices and Procedures

• Presence of invasive devices: 1, 3
  • Intravenous catheters (4.7-fold increased risk)
  • Urinary catheters
  • Nasogastric or endotracheal tubes
  • Drains
  • Joint prosthetics
  • Dialysis catheters

Healthcare Environment

• Intensive care unit setting (26.9-fold increased risk within first four days) 3
• High local prevalence of MRSA (>30-50% of S. aureus isolates) 1
• Presence of multiple MRSA-colonized patients in the same unit 1
• Environmental contamination 1

Community-Related Risk Factors

Social and Behavioral 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

Other Risk Factors

• Post-influenza-like illness, particularly in patients with severe underlying disease 1

Clinical Implications

Understanding these risk factors is crucial for:

1. Early identification of patients at high risk for MRSA infection
2. Targeted surveillance in high-risk settings such as intensive care units
3. Empiric antibiotic coverage decisions for patients with suspected infection
4. Prevention strategies including:
   • Appropriate hand and skin hygiene
   • Cleaning and disinfecting shared equipment
   • Prompt treatment of skin wounds
   • Decolonization strategies for carriers (mupirocin nasal ointment, oral clindamycin)

The presence of multiple risk factors significantly increases the likelihood of MRSA infection and should prompt consideration of preventive measures and early empiric coverage when infection is suspected 1, 4.

Healthcare facilities should prioritize prevention of initial MRSA colonization in surgical and intensive care patients, as these populations are at highest risk for progression from colonization to clinical infection 3.

Patients with a history of MRSA who are discharged from the hospital remain at elevated risk for invasive MRSA infection for up to 100 days post-discharge, highlighting the need for continued vigilance during this period 2.