Performance Evaluation of STANDARD F Strep A Ag FIA for Diagnosis of Group A Streptococcal Pharyngitis

Seon A Jo¹ Sang Hyuk Ma² Seungjun Lee³ Sunjoo Kim^34*

¹ Department of Laboratory Medicine, Daewoo General Hospital, Geoje
² Department of Pediatrics,Changwon Fatima Hospital, Changwon
³ Department of Laboratory Medicine, Gyeongsang National University Changwon Hospital, Changwon
⁴ Gyeongsang National University, Gyeongsang Institute of Health Sciences, Jinju

Abstract

Background: Pharyngitis is one of the most common conditions encountered in primary health care facilities. Accurate differentiation of group A streptococcus (GAS) infection from viral infection is difficult. The STANDARD F Strep A Ag FIA (SD BIOSENSOR, Korea) is a rapid antigen detection test (RADT) that has been recently developed for diagnosing GAS pharyngitis. In this study, we evaluated the diagnostic performance of the STANDARD F Strep A Ag FIA and compared the results between the RADT and conventional throat culture.

Methods:Throat swab samples were obtained from a total of 372 children presenting pharyngitis symptoms in five pediatric clinics in Changwon, Korea from July 2018 to October 2019. A comparative study between STANDARD F Strep A Ag FIA and Sofia Strep A FIA (Quidel, USA) was performed. Two throat swabs were taken simultaneously from each patient for RADT. The third throat swab was stored in a transport tube containing Stuart's transport medium for culture. Performance and kappa index of STANDARD F Strep A Ag FIA were evaluated.

Results: GAS infection was detected in 29.3% (109/372) patients, using the STANDARD F Strep A Ag FIA. The sensitivity, specificity, positive predictive value, and negative predictive value were 95.0%, 95.2%, 88.1%, and 98.1%, respectively. The STANDARD F Strep A Ag FIA showed an excellent concordance rate of 96.5% and a kappa value of 0.89 compared to Sofia Strep A FIA.

Conclusion: The STANDARD F Strep A Ag FIA demonstrated an excellent performance along with Sofia Strep A FIA for the diagnosis of GAS pharyngitis.

Keywords

Group A streptococcus Pharyngitis Rapid antigen test Streptococcus pyogenes Tonsillitis

Figures & Tables

Fig. 1. Distribution of age and sex of STANDARD F Strep A Ag FIA positive patients.

Figures & Tables

Table 1. Clinical performance of STANDARD F Strep A Ag FIA and Sofia Strep A FIA compared to throat culture

Rapid antigen detection tests	Results	Throat culture	Sensitivity (95% CI)	Specificity (95% CI)
GAS Positive	GAS Negative
STANDARD F Strep A Ag FIA	Positive	96	13	95.0% (88.8-98. 4%)	95.2% (91.9-97. 4%)
	Negative	5	258
SOFIA Strep A FIA	Positive	95	11	94.1% (87.5-97. 8%)	95.9% (92.9-98. 0%)
	Negative	6	260