[Clinical application and diagnostic value of 3 detection methods for acute pharyngitis of group A

Objective: Using bacterial culture as the gold standard, to evaluate the agreement of rapid antigen detection test (RADT) and rapid nucleic acid test (RNAT) in diagnosing group A Streptococcus (GAS) pharyngitis in pediatric outpatients, and assess their potential clinical utility. Methods: This cross-sectional study prospectively collected throat swab specimens and clinical data of 338 children diagnosed with acute pharyngitis at the Department of Outpatient Beijing Children's Hospital, Capital Medical University, between July 2023 and February 2024. The specimens were tested for GAS bacterial culture, RADT and RNAT. Using bacterial culture results as the reference standard, Kappa consistency analysis was performed to assess the diagnostic concordance between RADT and RNAT. Chi-square test was used to compare clinical characteristics between cases diagnosed by different methods. Results: In the 338 children diagnosed with pharyngitis, 195 were male and 143 were female, with an age at the visit of 7.4 (5.9, 7.4) years. The positivive rates for GAS detection were 25.7% (87/338) by bacterial culture, 20.7% (70/338) by RADT, and 41.7% (141/338) by RNAT. In terms of diagnostic performance, RADT exhibited a higher specificity (96.8% (243/251)) and better agreement with bacterial culture results (κ=0.73), whereas RNAT showed greater sensitivity (95.4% (83/87)) but lower specificity (76.9% (193/251)) and moderate agreement (κ=0.61). Among the 87 children with positive bacterial culture for GAS, 56 were male and 31 were female, with an age at visit of 7.3 (6.2, 8.8) years. Clinically, fever predominantly ranged from 38.1 to 39.0 ℃ 48 cases (55.2%), and common accompanying symptoms included sore throat 62 cases (71.3%), cough 33 cases (37.9%), and cervical lymphadenopathy or tenderness 16 cases (18.4%). On physical examination, tonsillar enlargement was present in 73 cases (83.9%) and exudate in 37 cases (42.5%). The McIsaac score was most frequently 4 points, observed in 37 cases (42.5%). Laboratory tests showed a peripheral white blood cell (WBC) count of 14.5 (12.3, 18.7)×10⁹/L and C-reactive protein (CRP) concentration of 22.0 (10.1, 41.4) mg/L. There were no statistically significant differences in the proportion of fever, sore throat, cough, tender cervical lymphadenopathy, tonsillar exudates, or tonsillar enlargement, nor in WBC count or CRP, among children who tested positive by RADT, RNAT, or bacterial culture (all P>0.05). Conclusions: Compared with bacterial culture,the RADT demonstrates higher specificity, while the RNAT exhibits greater sensitivity. Both methods show good concordance with culture results and may serve as effective adjunctive tools for the early screening of GAS pharyngitis.