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

Risk Factors for Developing MRSA

Previous MRSA infection or colonization within the past year is the single most reliable predictor for developing MRSA infection, and should be the first factor assessed in any patient. 1, 2

Healthcare Exposure Risk Factors

Prior Healthcare Contact

• Recent hospitalization within the preceding 12-24 months significantly increases 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
• Prolonged hospital stays, particularly in intensive care units, substantially elevate risk 3, 4
• ICU patients have a 26.9-fold higher rate of developing MRSA infection within the first four days compared to medical ward patients 5

Recent Antibiotic Exposure

• Antibiotic use within the past 3-12 months, particularly beta-lactams, carbapenems, or quinolones, is a critical risk factor 1, 2
• Intravenous antibiotic treatment within the prior 90 days specifically increases risk in hospital-acquired pneumonia 2
• Use of three or more antibiotics during hospitalization increases infection rates 5
• Previous antibiotic use is an independent risk factor with an odds ratio of 2.337 4

Medical Comorbidities

Chronic Diseases

• Diabetes mellitus, particularly in diabetic foot infections, is a significant independent risk factor 1, 6, 2
• Chronic kidney disease requiring hemodialysis substantially increases risk and is an independent predictor on multivariable analysis 1, 6, 2
• Congestive heart failure is associated with higher MRSA risk 6, 2
• Chronic obstructive pulmonary disease (COPD) increases susceptibility 6
• Chronic liver failure elevates vulnerability 6, 2

Immunosuppression

• Immunosuppression from any cause (disease or medication-related) significantly increases MRSA risk 6, 2
• HIV infection is associated with higher MRSA rates 6, 2
• Chemotherapy-induced neutropenia requires empiric MRSA coverage when skin/soft tissue inflammation is present or the patient is hemodynamically unstable 2

Invasive Devices and Procedures

Indwelling Devices

• Presence of central venous catheters is an independent risk factor with an odds ratio of 4.7 and 1.822 in different studies 5, 4
• Hemodialysis catheters increase risk 1, 6
• Urinary catheters elevate infection rates 1, 5
• Endotracheal tubes and mechanical ventilation are significant risk factors 1, 5, 4
• Nasogastric tubes increase susceptibility 1, 5
• Presence of surgical drains elevates risk 1, 5

Wounds and Skin Breakdown

• Surgical wounds are an independent risk factor with a hazard ratio of 2.9 5
• Pressure ulcers (decubitus ulcers) are an independent risk factor with a hazard ratio of 3.0 5, 7
• Open wounds or chronic skin lesions increase MRSA risk 1, 6, 8
• Chronic ulcers of any type elevate susceptibility 1, 5

Clinical Severity Indicators

Acute Illness Severity

• Septic shock in the context of pneumonia warrants empiric MRSA coverage regardless of other risk factors 2
• Need for ventilatory support due to pneumonia is a mortality risk factor requiring MRSA coverage 2
• Respiratory failure significantly increases risk 8
• Bacteremia, where 49.6% of S. aureus coinfections are MRSA, requires immediate empiric coverage 1, 2

Additional Severity Markers

• Receipt of blood transfusion is associated with higher MRSA infection rates 8
• Difficulty swallowing increases risk, particularly in ICU patients 8
• Total parenteral nutrition administration elevates susceptibility 6, 4

Local Epidemiology Considerations

Empiric MRSA coverage should be initiated when local MRSA prevalence exceeds specific thresholds: 50% of S. aureus isolates for mild soft tissue infections, 30% for moderate infections, or 20% in hospital-acquired pneumonia settings. 1, 2

• High local prevalence in a specific ICU or hospital unit is a risk factor 1
• Presence of more than 2 patients with nasal MRSA colonization in the same ICU at the same time is an independent risk factor with an odds ratio of 1.398 4

Community-Associated MRSA Risk Factors

Special Populations

• Children under 2 years old are at increased risk 6
• Athletes, particularly contact-sport participants, have elevated risk 6
• Injection drug users face substantially higher risk 6
• Homosexual males are at increased risk 6
• Military personnel have higher susceptibility 6
• Inmates of correctional facilities, residential homes, or shelters are at elevated risk 6
• Veterinarians, pet owners, and pig farmers have occupational exposure risk 6

Critical Pitfalls to Avoid

• Do not assume that community-acquired and healthcare-acquired MRSA are distinct entities—the distinction has become increasingly blurred 6
• In ICU patients colonized with MRSA, prior history of MRSA, difficulty swallowing, presence of an open wound, and central line placement are specific risk factors for progression to infection 8
• Patients colonized with MRSA who have surgical wounds, pressure ulcers, or intravenous catheterization should receive priority for infection prevention measures, as these are independent risk factors for progression from colonization to infection 5
• Transfer from a nursing home is a significant risk factor that is often underappreciated 8
• Prolonged hospitalization (duration in ICU) is an independent risk factor with an odds ratio of 1.090 per day 4