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Updated: Aug 23, 2025
Subcutaneous Infection of Methicillin Resistant Staphylococcus Aureus MRSA
Published on: February 9, 2011
International Validation of a Methicillin-Resistant Staphylococcus aureus Risk Assessment Tool for Skin and Soft
E J Zasowski1,2,3,4, T D Trinh1,4, K C Claeys1,5
1Anti-Infective Research Laboratory, Department of Pharmacy Practice, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Ave, Detroit, MI, 48201, USA.
Introduction:
To promote judicious prescribing of methicillin-resistant Staphylococcus aureus (MRSA)-active therapy for skin and soft tissue infections (SSTI), we previously developed an MRSA risk assessment tool. The objective of this study was to validate this risk assessment tool internationally.
Methods:
A multicenter, prospective cohort study of adults with purulent SSTI was performed at seven international sites from July 2016 to March 2018. Patient MRSA risk scores were computed as follows: MRSA infection/colonization history (2 points); previous hospitalization, previous antibiotics, chronic kidney disease, intravenous drug use, human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), diabetes with obesity (1 point each). Predictive performance of MRSA surveillance percentage, MRSA risk score, and estimated MRSA probability (surveillance percentage adjusted by risk score) were quantified using the area under the receiver operating characteristic curves (aROC) and compared. Performance characteristics of different risk score thresholds across varying baseline MRSA prevalence were examined.
Results:
Two hundred three patients were included. Common SSTI were wounds (28.6%), abscess (25.1%), and cellulitis with abscess (20.7%). Patients with higher risk scores were more likely to have MRSA (P < 0.001). The MRSA risk score aROC (95%CI) [0.748 (0.678-0.819)] was significantly greater than MRSA surveillance percentage [0.646 (0.569-0.722)] (P = 0.016). Estimated MRSA probability aROC [0.781 (0.716-0.845)] was significantly greater than surveillance percentage (P < 0.001) but not the risk score (P = 0.192). The estimated negative predictive value (NPV) of an MRSA score ≥ 1 (i.e., a score of 0) was greater than 90% when MRSA prevalence was 30% or less.
Conclusion:
The MRSA risk score and estimated MRSA probability were significantly more predictive of MRSA compared with surveillance percentage. An MRSA risk score of zero had high predictive value and could help avoid unnecessary empiric MRSA coverage in low-acuity patients. Further study, including impact of such risk assessment tools on prescribing patterns and outcomes are required before implementation.
Insights
A validated MRSA risk score accurately predicts methicillin-resistant Staphylococcus aureus in skin infections. A score of zero suggests low risk, potentially avoiding unnecessary antibiotic treatment.
Area of Science:
- Infectious Diseases
- Clinical Microbiology
- Pharmacology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant challenge in treating skin and soft tissue infections (SSTIs).
- Judicious prescribing of MRSA-active therapy is crucial to combat antimicrobial resistance.
- A previously developed MRSA risk assessment tool required international validation.
Purpose of the Study:
- To validate an existing MRSA risk assessment tool internationally.
- To evaluate the predictive performance of the tool for MRSA in patients with SSTI.
Main Methods:
- A multicenter, prospective cohort study involving adults with purulent SSTI across seven international sites.
- Calculation of MRSA risk scores based on patient history (infection/colonization, hospitalization, antibiotics, comorbidities).
- Comparison of predictive performance using area under the receiver operating characteristic curves (aROC) for risk score, surveillance percentage, and estimated MRSA probability.
Main Results:
- Higher MRSA risk scores correlated significantly with MRSA presence (P < 0.001).
- The MRSA risk score (aROC: 0.748) and estimated MRSA probability (aROC: 0.781) were significantly more predictive than surveillance percentage (aROC: 0.646).
- An MRSA risk score of 0 demonstrated a negative predictive value >90% when MRSA prevalence was ≤30%.
Conclusions:
- The MRSA risk score and estimated MRSA probability offer superior prediction of MRSA compared to surveillance percentages.
- A risk score of zero indicates low MRSA likelihood, potentially reducing unnecessary empiric MRSA coverage in select patients.
- Further research is needed to assess the impact of this tool on prescribing patterns and clinical outcomes before widespread implementation.
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