Changing Patterns of Infectious Diseases Among Hospitalized Children in Hokkaido, Japan, in the Post-COVID-19 Era, July 2019 to June 2022

Yuya Fukuda, Atsuo Togashi, Satoshi Hirakawa, Masaki Yamamoto, Shinobu Fukumura, Tomohiro Nawa, Saho Honjo, Jun Kunizaki, Kouhei Nishino, Toju Tanaka, Toshitaka Kizawa, Dai Yamamoto, Ryoh Takeuchi, Yuta Sasaoka, Masayoshi Kikuchi, Takuro Ito, Kazushige Nagai, Hirofumi Asakura, Katsumasa Kudou, Masaki Yoshida, Takeshi Nishida, Takeshi Tsugawa

Many reports have reported a reduction in respiratory infectious diseases and infectious gastroenteritis immediately after the coronavirus disease 2019 (COVID-19) pandemic, but data continuing into 2022 are very limited. We sought to understand the current situation of various infectious diseases among children in Japan as of July 2022 to improve public health in the post-COVID-19 era. We collected data on children hospitalized with infectious diseases in 18 hospitals in Japan from July 2019 to June 2022. In total, 3417 patients were hospitalized during the study period. Respiratory syncytial virus decreased drastically after COVID-19 spread in early 2020, and few patients were hospitalized for it from April 2020 to March 2021. However, an unexpected out-of-season re-emergence of respiratory syncytial virus was observed in August 2021 (50 patients per week), particularly prominent among older children aged 3-6 years. A large epidemic of delayed norovirus gastroenteritis was observed in April 2021, suggesting that the nonpharmaceutical interventions for COVID-19 are less effective against norovirus. However, influenza, human metapneumovirus, Mycoplasma pneumoniae, and rotavirus gastroenteritis were rarely seen for more than 2 years. The incidence patterns of various infectious diseases in Japan have changed markedly since the beginning of the COVID-19 pandemic to the present. The epidemic pattern in the post-COVID-19 era is unpredictable and will require continued careful surveillance.