Background: Streptococcus pyogenes (Group A streptococcus, GAS) is the most common cause of bacterial pharyngitis. This study aims to identify the clinical characteristics for diagnosing streptococcus pharyngitis. Also I conducted microbiological and molecular genetics research on cultured strains.
Methods: A total of 372 children, who had pharyngitis symptoms or signs, were subjected to throat cultures and rapid antigen detection test (RADT). I analyzed the correlation between clinical symptoms and RADT. Antimicrobial susceptibility test was performed for erythromycin (ERY), clindamycin (CLI), tetracycline (TET) and ofloxacin (OFX). Screenings for macrolide resistance phenotype and its determinants were tested for the ERY-resistant two strains. emm genotyping was conducted by PCR and direct sequencing. The emm genotypes were assigned according to the web-based database.
Results: Of all the 372 throat swab specimens, 101 (27.2%) were positive for GAS by culture and 106 (28.5%) were positive for GAS by RADT. The performance of RADT compared to culture was 94.1%, 95.9%, 89.6% and 97.7%, respectively, for sensitivity, specificity, positive predictive value (PPV), and negative predictive value value (NPV). This study was conducted on 205 patients with all clinical evidence recorded. The clinical manifestations such as pharyngeal and palatal hemorrhage, tonsillar swelling, rash, and enlarged cervical nodes were statistically significant in the diagnosis of GAS pharyngitis. The resistant rates to ERY, CLI, TET and OFX were 2.0%, 2.0%, 0% and 2.0%, respectively. There were two isolates of the cMLSB phenotype with the ermB gene in the two ERY-resistant strains. The emm analysis was performed on 59 of 101 among the surviving strains. The most frequent type was emm89 (20.3%), followed by 12 (16.9%), 4 (13.6%), 28 (11.9%), 3 (10.2%).
Conclusions: This study identified statistically significant symptoms and signs for clinical diagnosis of GAS pharyngitis. However, using RADT, more accurate, convenient and objective GAS diagnosis is possible. The database of emm genotype of GAS can be used as epidemiological data of GAS infection[1-3].