Epidemiology and clinical characteristics of invasive group A streptococcal infection in the Republic of Korea, 2015–2024: a nationwide multicenter study

Background: Invasive group A streptococcal (iGAS) infection has resurged globally following the coronavirus disease 2019 pandemic; however, long-term nationwide data from Asia is limited. This study aimed to investigate the epidemiology, clinical burden and molecular characteristics of iGAS infection in the Republic of Korea (ROK) over a 10-year period. Methods: A nationwide multicentre study for iGAS was conducted across 23 university-affiliated hospitals from 2015 to 2024. iGAS was defined as culture-confirmed isolation of Streptococcus pyogenes from sterile sites. Clinical data were collected using standardised forms. Available isolates were emm-typed and whole genome sequencing was performed for emm1 isolates. Findings: A total of 454 iGAS cases were identified. The mean annual incidence was 4.72/100,000 admissions (95% CI 4.26–5.13), declining from 7.03 (95% CI 6.26–7.77) in 2015–2019 to 1.72 (95% CI 1.27–2.26) in 2020–2022. In 2023–2024, the incidence returned to pre-pandemic levels among children (10.45 per 100,000 admissions, 95% CI 5.95–14.39), whereas the adult incidence partially recovered (2.47 per 100,000 admissions, 95% CI 1.76–3.33). Skin and soft tissue infection (22.7%), streptococcal toxic shock syndrome (STSS, 19.6%), and bacteremia without focus (17.0%) were the most common iGAS infections. Intensive care unit admission was required in 28.9% of iGAS cases, and overall mortality was 15.5%. Mortality was independently associated with STSS (aOR 20.07, 95% CI 9.30–43.30; p < 0.0001), older age (aOR 20.07, 95% CI 9.30–43.30; p < 0.0001), chronic medical condition (aOR 2.96, 95% CI 1.41–6.22; p = 0.004), and immunocompromised condition (aOR 2.33, 95% CI 1.07–5.09; p = 0.034) among adults. Among 98 isolates, the predominant strains were emm1 (32/98, 32.7%), emm12 (13/98, 13.3%), emm28 (11/98, 11.2%), and emm89 (8/98, 8.2%). Of 32 emm1 isolates, two (6.3%) isolates belonged to the epidemic M1UK lineage were identified (2020, 2024). Interpretation: Following marked pandemic-associated suppression, iGAS incidence rapidly rebounded among children in the ROK. This study reports the first detection of the M1UK lineage in the ROK, highlighting the need for statutory notification of iGAS as a nationally notifiable disease to enable continuous national surveillance with molecular characterization for monitoring emerging epidemic-prone strains. Funding: This work was supported by the Korea Disease Control and Prevention Agency.