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

MRSA Risk Factors

Healthcare-Associated Risk Factors

The most reliable predictor for MRSA infection is previous MRSA infection or colonization within the past year 1, 2. Beyond this, healthcare exposures constitute the primary risk category for MRSA acquisition.

Recent Healthcare Exposures

• Prior 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
• Recent antibiotic exposure within 3-12 months, particularly beta-lactams, carbapenems, or quinolones, substantially increases risk 3, 1, 2
• Intravenous antibiotic treatment within the prior 90 days is specifically associated with MRSA in hospital-acquired pneumonia 3

Invasive Devices and Procedures

• Presence of central venous catheters carries a hazard ratio of 4.7 for progression from colonization to infection 4, 1, 2
• Hemodialysis catheters, urinary catheters, endotracheal tubes, nasogastric tubes, or drains all increase MRSA risk 1, 2, 4
• Recent invasive procedures or surgery are independent risk factors, with surgical wounds carrying a hazard ratio of 2.9 1, 4, 5
• Implantable cardiac devices increase risk and warrant consideration for transesophageal echocardiography if bacteremia develops 6

Critical Care Setting

• Intensive care unit admission confers a hazard ratio of 26.9 for developing MRSA infection within the first four days compared to medical ward patients 4
• Treatment in units where MRSA prevalence exceeds 20% of S. aureus isolates warrants empiric MRSA coverage 3, 2

Medical Comorbidities

High-Risk Chronic Conditions

• Diabetes mellitus, particularly in the context of foot infections, is a significant independent risk factor 1, 5
• Chronic kidney disease requiring hemodialysis substantially increases risk, with dialysis during follow-up being an independent predictor on multivariable analysis 1, 5
• Chronic obstructive pulmonary disease (COPD) increases MRSA susceptibility 1
• Congestive heart failure is associated with higher MRSA risk 1
• Chronic liver failure increases vulnerability to MRSA 1
• Hemiplegia is an independent risk factor on multivariable analysis 5

Immunocompromised States

• Immunosuppression from any cause (disease or medication-related) significantly increases MRSA risk 1
• HIV infection is associated with higher MRSA rates 1
• Chemotherapy-induced neutropenia requires empiric MRSA coverage when skin/soft tissue inflammation is present, the patient is hemodynamically unstable, or MRSA risk factors exist 3

Wounds and Skin Breakdown

• Pressure ulcers carry a hazard ratio of 3.0 for progression to MRSA infection 4, 1
• Open wounds, surgical wounds, chronic skin lesions, or ulcers all increase MRSA risk 1, 2, 4
• Necrotizing pancreatitis is associated with increased MRSA susceptibility 1

Community-Associated Risk Factors

Special Populations

• Injection drug users are at substantially elevated risk for community-associated MRSA 1, 7, 6
• Children under 2 years old have increased community-associated MRSA risk 1
• Athletes participating in contact sports are at higher risk 1
• Homosexual males have elevated community-associated MRSA rates 1
• Military personnel face increased exposure 1
• Inmates of correctional facilities, residential homes, or shelters are at high risk 1, 7
• Veterinarians, pet owners, and pig farmers have occupational exposure risk 1
• Homeless individuals are at increased risk 7

Social Risk Factors

The combination of homelessness, jail stay, promiscuity, intravenous drug use, and other drug use represents a latent variable with a relative risk of 3.14 for admission MRSA 7.

Clinical Severity Indicators

High-Risk Clinical Presentations

• Septic shock in the context of pneumonia warrants empiric MRSA coverage regardless of other risk factors 3, 2
• Need for ventilatory support due to pneumonia is a mortality risk factor requiring MRSA coverage 3
• Bacteremia, where 49.6% of S. aureus coinfections are MRSA, requires immediate empiric coverage 2, 6
• Severe infections where treatment failure would pose unacceptable risk should receive empiric MRSA therapy regardless of other factors 2, 8

Healthcare-Associated Intra-Abdominal Infection

Empiric MRSA coverage is indicated for patients with healthcare-associated intra-abdominal infection who are known MRSA carriers or have prior treatment failure with significant antibiotic exposure 3.

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 3, 2, 8.

Critical Pitfall

The distinction between healthcare-associated and community-associated MRSA has become increasingly blurred, as community-associated strains have moved into nosocomial settings, limiting the utility of clinical risk factors alone to designate infection type 1, 9. This means traditional healthcare exposure criteria may underestimate MRSA risk in certain populations, particularly injection drug users and those with social risk factors.