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

MRSA Risk Factors

Previous MRSA infection or colonization within the past year is the single most reliable predictor for MRSA infection, and should be the primary screening question when assessing risk. 1, 2

Healthcare-Associated Risk Factors

The following healthcare exposures substantially increase MRSA risk and should trigger consideration of empiric coverage:

• Prior hospitalization within the preceding 12-24 months significantly elevates MRSA risk 1, 2
• Residence in long-term care facilities or rehabilitation centers within the last 18 months is a major risk factor 1, 2
• Recent antibiotic exposure within 3-12 months, particularly beta-lactams, carbapenems, or quinolones, substantially increases risk 1, 2
• Intravenous antibiotic treatment within the prior 90 days is specifically associated with MRSA in hospital-acquired pneumonia 1
• Treatment in units where MRSA prevalence exceeds 20% of S. aureus isolates warrants empiric MRSA coverage according to the Infectious Diseases Society of America 1

Medical Comorbidities and Chronic Conditions

Multiple underlying conditions independently increase MRSA susceptibility:

• Diabetes mellitus, particularly in the context of foot infections, is a significant independent risk factor 1, 2, 3
• Chronic kidney disease requiring hemodialysis substantially increases risk, with dialysis during follow-up being an independent predictor on multivariable analysis 1, 2, 3
• Congestive heart failure is associated with higher MRSA risk 1
• Chronic liver failure increases vulnerability to MRSA 1
• Immunosuppression from any cause significantly increases MRSA risk 1, 2
• HIV infection is associated with higher MRSA rates 1
• Hemiplegia emerged as an independent risk factor in multivariable analysis 3

Invasive Devices and Procedural Risk Factors

The presence of invasive devices creates direct portals for MRSA entry:

• Central venous catheters, hemodialysis catheters, and urinary catheters are risk factors for MRSA infection 2, 4
• Endotracheal tubes, nasogastric tubes, or drains increase MRSA risk 2, 4, 5
• Intravenous catheterization is an independent risk factor with a hazard ratio of 4.7 5
• Open wounds or skin breakdown, including surgical wounds, pressure ulcers, chronic skin lesions, or ulcers, are significant risk factors 2, 5
• Surgical wounds carry a hazard ratio of 2.9 for progression from colonization to infection 5
• Pressure ulcers have a hazard ratio of 3.0 for developing active MRSA infection 5
• Recent surgery during follow-up is an independent predictor on multivariable analysis 3

Clinical Severity Indicators Requiring Immediate Empiric Coverage

Certain clinical presentations mandate empiric MRSA therapy regardless of other risk factors:

• Septic shock in the context of pneumonia warrants empiric MRSA coverage regardless of other risk factors 1, 2
• Need for ventilatory support due to pneumonia is a mortality risk factor requiring MRSA coverage 1
• Bacteremia, where 49.6% of S. aureus coinfections are MRSA, requires immediate empiric coverage 1, 2
• Severe infections where treatment failure would pose unacceptable risk should receive empiric MRSA therapy regardless of other factors 1, 2

Special Population Risk Factors

• Chemotherapy-induced neutropenia requires empiric MRSA coverage when skin/soft tissue inflammation is present, the patient is hemodynamically unstable, or MRSA risk factors exist according to the National Comprehensive Cancer Network 1
• Intravenous drug use is the only independent risk factor that correlated with community-acquired MRSA hand infections in multivariable analysis 6
• Intensive care setting confers a hazard ratio of 26.9 for developing MRSA infection within the first four days compared to medical patients 5
• Trauma or medical patients have increased risk compared to surgical patients 4

Local Epidemiology Thresholds

The Centers for Disease Control and Prevention provides specific prevalence thresholds that should trigger empiric MRSA coverage:

• ≥50% of S. aureus isolates for mild soft tissue infections 1, 2
• ≥30% of S. aureus isolates for moderate infections 1
• ≥20% of S. aureus isolates in hospital-acquired pneumonia settings 1
• High local prevalence in a specific ICU or hospital unit should influence empiric therapy decisions 2

Common Pitfalls

A critical caveat: while these risk factors are well-established, research demonstrates that clinical-demographic risk factors alone should not be used to accurately identify patients who would benefit from empirical anti-MRSA treatment, as the best predictive models achieve only 67% sensitivity and 76.5% specificity 4. Therefore, when multiple risk factors are present or infection severity is high, empiric MRSA coverage should be initiated rather than waiting for culture confirmation.