Clinical and microbiological characterization of invasive group a Streptococcus infection in children in Japan: A single-center experience.

Background: Invasive group A Streptococcus (iGAS) infections are rare but potentially fatal. Although the number of invasive group A Streptococcus (iGAS) infections decreased during the coronavirus disease (COVID-19) pandemic, it sharply increased worldwide following the pandemic due to the emergence of M1 strains. In Japan, non-fluminant iGAS infections have not been included in the national survey notification system. Therefore, the clinical and microbiological characteristics of iGAS infection are unknown. In this study, we aimed to clarify the clinical and microbiological characteristics of pediatric iGAS infections.

Methods: We conducted a case-series analysis of children aged 0-15 years with positive Streptococcus pyogenes cultures from otherwise sterile sites, diagnosed between July 2018 and June 2024. Clinical data were extracted from the electronic medical records. Samples of clinical isolates were sent to the Public Health Research Institute for further analysis.

Results: We identified 11 patients (median age, 5 years [interquartile range 1-8.5 years]; 6 girls). The incidence rate of the iGAS infections was highest in 2024, with 3 cases in 6 months. Primary bacteremia without focal infection was the predominant diagnosis, followed by skin and soft tissue infections with bacteremia. Among the 11 iGAS infections, 9 isolates were available for additional microbiological tests. M12 and M1 strains were predominant (four cases each). Three of the four M1 isolates were M1 strains.

Conclusions: In the present study, the increasing incidence of iGAS infection and clinical diagnoses are similar to those reported in other countries; however, M12 strains as well as M1 strains are predominant.