Trends in the growing impact of group A Streptococcus infection on public health after COVID-19 pandemic: a multicentral observational study in Okayama, Japan.

Purpose: Following the COVID-19 pandemic, group A Streptococcus (GAS) infection has been surging worldwide. We aimed to compare the disease burden between notified cases of streptococcal toxic shock syndrome (STSS) and unreported GAS infections.

Methods: This is a multicentral observational study, retrospectively performed at seven hospitals in Okayama prefecture in Japan from January 2022, to June 2024. Clinical and microbiological data of patients with positive cultures of GAS were collected from the medical records. Primary outcomes were defined as rates of surgical procedures, intensive care unit (ICU) admission, and in-hospital mortality, which were compared among patients with locally-defined STSS, invasive GAS (iGAS), and non-iGAS infection.

Results: GAS was detected in 181 patients, with 154 active cases of GAS infection. The number of patients with GAS infection surged in late 2023. The most common source of infection was skin and soft tissue infections, accounting for 83 cases, including 15 cases of necrotizing fasciitis, and 12 cases (7.8%) were notified to public health authorities as STSS. Among the 25 unreported iGAS cases, 9 (36.0%) underwent surgical intervention, and 4 patients (16.0%) required ICU admission. The mortality rates in the unreported iGAS cases were comparable to those observed in the notified STSS.

Conclusions: We highlighted that the number of iGAS infections was twofold higher than that of notified STSS, with comparable mortality rate between these groups, indicating substantial underestimation of the true burden of iGAS. This epidemiological investigation has significant implications for enhancing infectious disease surveillance frameworks and public health policy development.