Post-pandemic surge in invasive group A Streptococcus infections: A hospital-based active surveillance study in Okinawa, Japan.

BACKGROUND

Invasive group A Streptococcus (iGAS) infections have increased worldwide following the COVID-19 pandemic, whereas recent clinical and molecular characteristics in Japan remain unclear.

METHODS

We conducted a hospital-based descriptive study of iGAS cases identified through active surveillance in Okinawa, Japan, from January 2023 to May 2025. Hospitalized patients with Streptococcus pyogenes isolated from normally sterile sites were included. Clinical data were retrospectively collected, and emm genotyping with detection of streptococcal pyrogenic exotoxin genes was performed.

RESULTS

A total of 26 cases were identified (median age, 8.5 years; interquartile range, 3.3-43 years), including 15 pediatric patients. Fever occurred in 25 cases, and shock developed in 5. The most common diagnoses were chest infections (n = 8, including 7 empyema) and skin and soft tissue infections (n = 8). Blood cultures were positive in 14 of 24 tested cases. Two fatal cases occurred in adults, whereas none occurred in children. Of the 6 pediatric empyema cases, 4 were associated with viral co-infections. All empyema patients required chest tube drainage and surgery. The predominant emm genotype was emm1.0 (18/26), followed by emm4.0 (2/26); among emm1.0 isolates, 7 were M1UK and 9 were M1global.

CONCLUSIONS

Recent iGAS cases were characterized by pediatric empyema frequently associated with viral co-infections and diverse emm lineages, suggesting that the post-pandemic surge was not driven by a single dominant clone.