Evaluation of the SD Bioline Strep A Ultra Test in Relation With Number of Colony Forming Units and Color Intensity

BACKGROUND: The SD Bioline Strep A Ultra (SD, Yongin, Korea) is a recently developed rapid antigen detection test (RADT) for diagnosing bacterial pharyngitis caused by Group A Streptococcus, We evaluated the performance of SD Bioline Strep A Ultra, using the number of colony forming units and color intensity. METHODS: Three throat swabs each were taken from 343 children with pharyngitis who visited pediatric clinics. We evaluated the performance of SD Bioline Strep A Ultra and compared its positive rate with the number of colony forming units, using the Fisher exact test. RESULTS: The sensitivity, specificity, positive predictive value, and negative predictive value (95% confidence interval) were 97.4% (94.0–99.1%), 90.8% (85.0–94.9%), 93.0% (88.5–96.1%), and 96.5% (92.0–98.9%), respectively. Positive rate significantly differed by number of colony forming units (P=0.021). ROC plot for color intensity showed 0.938 of AUC (area under curve). CONCLUSIONS: SD Bioline Strep A Ultra showed excellent performance, and its positive rate differed by the number of colony counts. This RADT could be used as a sensitive and semi-quantitative method detecting bacterial pharyngitis.