Analysis of Streptococcus pyogenes reinfection in pediatric patients in Japan

Acute pharyngitis and tonsillitis caused by Streptococcus pyogenes are common pediatric infectious diseases. Although the presence of penicillin-resistant S. pyogenes has not been confirmed in Japan, the re-isolation rate of S. pyogenes after antimicrobial treatment has been increasing. Thus, we attempted to determine whether the presence of S. pyogenes in pediatric patients treated with antimicrobial treatment was because of treatment failure or reinfection. We examined 19 patients who visited Daido Hospital between 2013 and 2017. The patient age, drug susceptibility patterns of the isolated bacteria, and random amplified polymorphic DNA (RAPD) analysis results were evaluated. The patient age ranged from 3 months to 9 years, seven patients were 5 years old. Seven patients showed consistent drug susceptible test results, and 12 patients showed inconsistent drug susceptible test results. Among these 12 patients, nine patients showed a greater decrease in drug susceptibility than the other three patients. Genetic mismatch was confirmed by RAPD analysis in all seven patients with consistent drug susceptible results. The paired S. pyogenes isolates from the same patient showed the presence of different bacteria. Our results indicate that, in many cases, re-isolation of S. pyogenes is not due to treatment failure, but due to reinfection with other clinical isolates.