Clinical Manifestations of Group A Streptococcal Pharyngitis and Comparison of Usefulness of Two Rapid Streptococcal Antigen Tests

ABSTRACT

BACKGROUND: Throat culture is the golden standard for diagnosis of group A streptococcal (GAS) pharyngitis. However, because it is a time-consuming procedure, antibiotics are often empirically administrated. Rapid antigen tests (RATs) can detect bacterial infections within 15 minutes, thus helping to reduce unnecessary administration of antibiotics. METHODS: In total, 108 patients, between 3 and 17 yr of age, who visited our hospital from August 2011 to July 2012, were tested for suspected acute pharyngitis with two RATs––SD Bioline Strep A (SD, Korea) and BinaxNOW Strep A (Binax, Inc., USA)––as well as throat culture. We compared the sensitivity, specificity, and consistency of the two RATs and assessed the clinical manifestations of GAS pharyngitis. RESULTS: Of the 108 patients, 15 were confirmed to have GAS pharyngitis by throat culture. The SD test showed a sensitivity of 93.3% and a specificity of 97.8%; the positive and negative predictive values were 87.5% and 98.9%, respectively. The Binax test showed a sensitivity of 86.7% and a specificity of 100%; the positive and negative predictive values were 100% and 97.9%, respectively. The Kappa values for conformity degree were high, 0.887 and 0.918 in the SD and the Binax tests, respectively (P=0.00). Clinical manifestation assessment of GAS pharyngitis indicated that scarlatiniform rash and strawberry tongue were significantly associated signs (P<0.05). CONCLUSIONS: GAS pharyngitis diagnosis based on clinical manifestations alone has practical limitations. The two RATs are useful as substitutes for throat culture and their frequent use in clinical settings is advisable.