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Updated: Aug 26, 2025
Subcutaneous Infection of Methicillin Resistant Staphylococcus Aureus MRSA
Published on: February 9, 2011
Does a Positive Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Screen Predict the Risk for MRSA Skin and
Allison M Hitchcock1, Robert W Seabury1, Wesley D Kufel1,2
1Department of Pharmacy, Upstate University Hospital, Syracuse, NY, USA.
Background:
Skin and soft tissue infections (SSTIs) are often caused by gram-positive bacteria that colonize the skin. Given the overuse of antibiotics, SSTIs are increasingly caused by resistant bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Guidance on the utility of MRSA nasal screening for MRSA SSTI is limited.
Objective:
To determine whether MRSA nasal screening predicts the risk of MRSA SSTIs.
Methods:
This was a single-center, retrospective cohort study of adult patients with an SSTI diagnosis that had MRSA nasal screening and wound cultures obtained within 48 hours of starting antibiotics. Sensitivity, specificity, positive and negative predictive value, and positive and negative likelihood ratios were calculated using VassarStats. Pretest and posttest probabilities were estimated with Microsoft Excel.
Results:
A total of 884 patient encounters were reviewed between December 1, 2018, and October 31, 2021, and 300 patient encounters were included. The prevalence of MRSA SSTI was 18.3%. The MRSA nasal colonization had a sensitivity of 63.6%, specificity of 93.9%, positive predictive value of 70.0% (95% CI = 55.2%-81.7%), negative predictive value of 92.0% (95% CI = 87.7%-94.9%), positive likelihood ratio of 10.39 (95% CI = 6.12-17.65), negative likelihood ratio of 0.39 (95% CI = 0.27-0.55), positive posttest probability of 70.0%, and negative posttest probability of 8.0%.
Conclusions:
Given the high positive likelihood ratio, a positive MRSA nasal screen was associated with a large increase in the probability of MRSA SSTI at our institution, and a negative MRSA nasal screen was associated with a small but potentially significant decrease in the probability of MRSA SSTI.
Insights
MRSA nasal screening can help predict the risk of methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTIs). A positive screen significantly increases MRSA SSTI probability, while a negative screen slightly decreases it.
Area of Science:
- Infectious Diseases
- Clinical Microbiology
- Epidemiology
Background:
- Skin and soft tissue infections (SSTIs) are frequently caused by Gram-positive bacteria.
- Antibiotic overuse has led to an increase in resistant pathogens, notably methicillin-resistant Staphylococcus aureus (MRSA).
- Limited guidance exists on the effectiveness of MRSA nasal screening for predicting MRSA SSTIs.
Purpose of the Study:
- To evaluate the predictive value of MRSA nasal screening for the development of MRSA SSTIs.
- To determine if nasal colonization status correlates with the risk of SSTIs caused by MRSA.
Main Methods:
- Retrospective cohort study of adult patients diagnosed with SSTI.
- Inclusion criteria: MRSA nasal screening and wound cultures within 48 hours of antibiotic initiation.
- Statistical analysis included sensitivity, specificity, predictive values, and likelihood ratios.
Main Results:
- The study reviewed 884 patient encounters, including 300 in the final analysis.
- MRSA SSTI prevalence was 18.3%.
- MRSA nasal screening demonstrated a sensitivity of 63.6%, specificity of 93.9%, positive predictive value of 70.0%, and negative predictive value of 92.0%.
Conclusions:
- A positive MRSA nasal screen significantly increases the likelihood of MRSA SSTI.
- A negative MRSA nasal screen is associated with a decreased, though potentially significant, probability of MRSA SSTI.
- Nasal MRSA screening provides valuable predictive information for MRSA SSTI risk assessment.
