MRSA Risk Factor Assessment Checklist
When evaluating any patient for MRSA risk, systematically assess the following categories to determine if empiric anti-MRSA coverage is warranted.
Healthcare Exposure History
Previous MRSA infection or colonization within the past year is the single most reliable predictor for MRSA infection 1, 2. Specifically document:
- Prior MRSA isolation from any site (especially respiratory specimens, which carries a 42.8% post-test probability of MRSA pneumonia) 3
- Recent hospitalization within the preceding 12-24 months 2, 4
- Long-term care facility or rehabilitation facility residence within the last 18 months 2, 4
- Recent antibiotic exposure within the past 3-12 months, particularly beta-lactams, carbapenems, or quinolones 2, 4
- ICU admission within the last 5 years 4
- Recent invasive procedures or surgical intervention within the last 60 months 4, 5
Current Clinical Setting
- Intensive care unit admission (hazard ratio 26.9 for developing MRSA infection within 4 days) 5
- Presence of invasive devices: central venous catheters (hazard ratio 4.7), hemodialysis catheters, urinary catheters, endotracheal tubes, nasogastric tubes, or drains 2, 4, 5
- Open wounds or skin breakdown: surgical wounds (hazard ratio 2.9), pressure ulcers (hazard ratio 3.0), chronic skin lesions, or ulcers 1, 2, 4, 5
High-Risk Comorbidities
Document presence of:
- Chronic kidney disease requiring hemodialysis 1, 2
- Diabetes mellitus (particularly relevant in foot infections) 1, 2
- Immunosuppression from disease or medications 2
- Chronic obstructive pulmonary disease 2
- Congestive heart failure 2
- Chronic liver failure 2
- HIV infection 2
- Comorbidity severity: APACHE class C or D or presence of fatal illness 4
Community-Associated MRSA Risk Factors
For patients without traditional healthcare exposures, assess:
- Age <2 years 2
- Contact sport participation (athletes) 2
- Injection drug use 2
- Incarceration in correctional facilities, residential homes, or shelters 2
- Military service 2
- Occupational exposure: veterinarians, pet owners, pig farmers 2
- Homosexual males 2
Local Epidemiology Considerations
Empiric MRSA coverage should be initiated when local MRSA prevalence exceeds specific thresholds 1:
- ≥50% of S. aureus isolates for mild soft tissue infections 1
- ≥30% of S. aureus isolates for moderate soft tissue infections 1
- High local prevalence in your specific ICU or hospital unit 1
Infection Severity Assessment
The severity of infection independently influences the decision to cover MRSA empirically 1:
- Severe infections where treatment failure would pose unacceptable risk warrant empiric MRSA coverage regardless of other risk factors 1
- Septic shock in the setting of pneumonia 1
- Bacteremia (63.4% of S. aureus coinfections in COVID-19 patients were bacteremic, with 49.6% being MRSA) 1
MRSA Nasal Screening Results
- Positive MRSA nasal screen on admission has a positive likelihood ratio of 6.9 and post-test probability of 20.7% 3
- Negative MRSA nasal screen has a negative likelihood ratio of 0.28 and post-test probability of only 1.04%, making MRSA CAP unlikely 3
- Consider nasal screening for high-risk patients to guide empiric therapy decisions 1
Common Pitfalls to Avoid
The distinction between healthcare-acquired and community-associated MRSA has become increasingly blurred 1, 2. Do not assume community-onset infections cannot be MRSA without assessing healthcare exposures 1.
Some patients may clinically improve despite MRSA isolation when treated with non-MRSA-active antibiotics 1, 2, but this should not be relied upon for empiric decision-making in high-risk patients 1.
In diabetic foot infections, MRSA prevalence ranges from 5-30%, and factors like long wound duration and presence of osteomyelitis increase risk 1. Always obtain bone specimens when osteomyelitis is suspected 1.
For surgical site infections, nasal colonization and recent hospitalization are more predictive than the surgical procedure type itself 1.