MRSA Risk Score Calculator

MRSA (methicillin-resistant Staphylococcus aureus) is a strain of staph that resists most beta-lactam antibiotics. Identifying patients at elevated risk for MRSA matters because empiric antibiotic choices for serious infections need to cover MRSA when the pretest probability is high — and avoid broad coverage when it is not, to limit resistance and side effects.

This calculator uses widely cited risk factors compiled from infection-control surveillance, IDSA guidelines, and several validation studies. Each present factor adds points to a running total. Higher scores predict higher likelihood of MRSA carriage on screening swabs and higher likelihood that a clinical infection (skin, soft tissue, bloodstream, pneumonia) is caused by MRSA.

Risk factors and weights:

• Known prior MRSA colonization or infection (+3): the strongest single predictor; previous carriers commonly recolonize even after decolonization protocols.
• Hospitalization in the past 90 days (+2): healthcare-associated MRSA exposure.
• Long-term care facility residence (+2): high baseline colonization rates in nursing facilities, often above 10% of residents.
• Antibiotics in the past 90 days (+1): selects for resistant flora by suppressing competing organisms.
• Hemodialysis (+2): repeated vascular access and frequent healthcare contact substantially raise risk.
• Indwelling vascular catheter or invasive device (+1): direct portal for skin organisms.
• Injection drug use (+2): community-associated MRSA strains circulate heavily in this population.
• Recent surgery (+1): transient skin and wound exposure.

Score interpretation (rough thresholds):

• 0-1 points: Low risk — empirical MRSA coverage usually unnecessary unless other clinical clues point to MRSA.
• 2-4 points: Moderate risk — consider MRSA coverage if a serious infection is suspected; consider screening culture.
• 5+ points: High risk — empirical MRSA coverage often indicated for significant infections; screening culture useful for ongoing care.

This score is a screening tool, not diagnostic. Local MRSA prevalence varies enormously between communities and hospitals — a moderate score in a high-prevalence environment carries different weight than the same score elsewhere. Always combine the score with local antibiogram data and clinical context before making antibiotic decisions.