Epidemiological characterization of Streptococcus pyogenes isolated from patients with multiple onsets of pharyngitis.

Streptococcus pyogenes causes a broad spectrum of acute infections and is the bacterium most frequently isolated from patients with pharyngitis. A number of antibiotics including penicillin have been shown to be effective, although antibiotic treatment failure in cases of streptococcal pharyngitis have been reported. Herein, we aimed to elucidate the features of recurrent strains using clinical isolates. Ninety-three S. pyogenes organisms were obtained from Japanese patients with recurrent pharyngitis. Following genetic characterization, M-type isolates from patients with recurrent pharyngitis differed from those obtained at initial onset in 11 of 49 episodes, and pulsed field gel electrophoresis analysis showed different patterns in those cases. Additionally, spe genotyping revealed that the Spe type of the strains obtained at secondary onset corresponded with those from the initial onset in 22 cases. Furthermore, antibiotic susceptibility testing revealed that more than half of the strains were resistant to macrolides and lincosamides, which was a much greater ratio as compared with the strains obtained from initial onsets in previous studies. Our results suggest that recurrence and reinfection are often confused during the diagnosis of repetitive and persistent streptococcal pharyngitis. Moreover, the present S. pyogenes organisms were less susceptible to antibiotics, which raises caution about their appropriate use in clinical practice.