Validation of a Clinical Decision Rule for Ultrasound Identification of MRSA Skin Abscesses in Children

Abstract

Objective The aim of this study was to validate an adult-derived clinical decision rule for ultrasound identification of methicillin-resistant Staphylococcus aureus (MRSA) skin abscesses in a pediatric cohort. Methods We conducted a retrospective study of skin and soft tissue infections in patients <21 years presenting to the emergency department who had radiology performed ultrasounds completed and wound cultures obtained. Ultrasound scans were reviewed for edge definition, volume, and shape by 2 pediatric emergency physicians with expertise in point-of-care ultrasound, with approximately 25% of scans reviewed by both experts to evaluate interrater reliability. A third, blinded expert weighed in for discrepancies before analysis. Test performance characteristics were calculated for the clinical decision rule in children. Results Two hundred nine patients were enrolled, with mean age of 9.8 (±6.7) years; 87 (42%) were male. Sixty-nine (33%) patients had a wound culture positive for MRSA. The clinical decision rule had a sensitivity of 86% (95% confidence interval [CI], 75%–93%), specificity of 32% (95% CI, 25%–41%), positive predictive value of 38% (95% CI, 35%–42%), negative predictive value of 82% (95% CI, 71%–89%), positive likelihood ratio of 1.26 (95% CI, 1.08–1.46), negative likelihood ratio of 0.45 (95% CI, 0.24–0.84), and an odds ratio of 2.8 (95% CI, 1.31–5.97). Conclusions This clinical decision rule for ultrasound identification of MRSA abscesses had moderately high sensitivity and negative predictive value in pediatric patients, with similar sensitivity compared with the original adult validation group. Ultrasound may help identify MRSA abscesses, allowing for improved antibiotic choices and outcomes for children with MRSA abscesses.