Trends in Group A <em>Streptococcus </em>Pharyngitis and Co-infection with Severe Acute Respiratory Syndrome Coronavirus 2: A Retrospective Observational Study

Background and Objectives: Group A Streptococcus (GAS) is a leading cause of acute pharyngitis with seasonal outbreaks in Japan. The coronavirus disease 2019 (COVID-19) pandemic significantly altered respiratory infection trends; however, its impact on GAS pharyngitis (GAS-P) remains unclear. Additionally, data on co-infections of GAS and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are limited. This study examined temporal trends in GAS-P incidence and characteristics of GAS–SARS-CoV-2 co-infections. Materials and Methods: We conducted this retrospective observational study at Tokyo Shinagawa Hospital between January 2019 and December 2024. Data on GAS and SARS-CoV-2 test results and patient demographics were extracted from medical records. The study period was categorized into three phases based on major public health policy changes: the pre-COVID social period (January 2019–April 2020), restricted social period (May 2020–April 2023), and post-restriction period (May 2023–December 2024). GAS positivity rates, age distributions, and case proportions were compared across these periods. Clinical characteristics of patients with concurrent GAS and SARS-CoV-2 infections were analyzed. Results: Among 4,837 GAS tests, 463 (9.6%) were positive. GAS positivity rates varied significantly: 11.4% (pre-COVID), 7.1% (restricted social period), and 12.6% (post-restriction period, p &amp;lt; 0.001). The proportion of pediatric cases decreased significantly during the restricted social period (24.8%–5.3%) before rising sharply in the post-restriction period (47.1%, p &amp;lt; 0.001). Among 151 patients tested for both GAS and SARS-CoV-2, 14 (9.3%) had co-infections, which were identified exclusively after July 2022. Most patients exhibited mild symptoms, primarily fever and sore throat, with decreased lymphocyte counts despite normal white blood cell levels. Conclusions: COVID-19-related infection control measures affected GAS-P incidence and age distribution, particularly the increase in pediatric cases post-restrictions. Limited testing may contribute to the underdiagnosis of GAS–SARS-CoV-2 co-infections. Further large-scale studies are warranted to assess microbial interactions, disease severity, and long-term outcomes.