Epidemiology of endemic human coronavirus infection during the COVID-19 pandemic.

INTRODUCTION: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the coronavirus family that also includes endemic human coronaviruses (HCoVs) types OC43, HKU1, 229E, and NL63. HCoVs share extensive sequence homology with SARS-CoV-2. It has been assumed that HCoV infection occur primarily in winter and spring in Japan before the coronavirus disease 2019 (COVID-19) pandemic and that its frequency is the same for all age groups. METHODS: Nasopharyngeal swab samples were collected for HCoVs and SARS-CoV-2. All medical data were retrospectively analyzed. Our primary objective was to describe the epidemiology of HCoV in the Furano, Japan during the COVID-19 pandemic. Our secondary objective was to compare the prevalence of HCoV with that of SARS-CoV-2. RESULTS: From September 2020 to August 2022, 113 (6.2 %) of 1823 cases were positive for any HCoV. The HCoV-NL63 activity peaked in January-March 2021. The HCoV-OC43 activity peaked in June-August 2021. HCoVs were mostly detected at age ≤11 years and most frequently at age ≤2 years. HCoVs showed high detection in 2021, while SARS-CoV-2 showed moderate detection in 2020-2021, but significantly increased in 2022. CONCLUSIONS: During the COVID-19 pandemic, HCoV-OC43 activity peaked in the summer. The frequency of HCoV infection varied widely by age group and was higher among those aged ≤11 years. These were different from those reported before the COVID-19 pandemic. These findings suggest that the disease dynamics of HCoVs remain unclear and that continued surveillance is essential in the post-COVID-19 pandemic.