BMC Infectious Diseases (Dec 2022)

Characteristics of hospitalized patients with COVID-19 during the first to fifth waves of infection: a report from the Japan COVID-19 Task Force

  • Ho Lee,
  • Shotaro Chubachi,
  • Ho Namkoong,
  • Takanori Asakura,
  • Hiromu Tanaka,
  • Shiro Otake,
  • Kensuke Nakagawara,
  • Atsuho Morita,
  • Takahiro Fukushima,
  • Mayuko Watase,
  • Tatsuya Kusumoto,
  • Katsunori Masaki,
  • Hirofumi Kamata,
  • Makoto Ishii,
  • Naoki Hasegawa,
  • Norihiro Harada,
  • Tetsuya Ueda,
  • Soichiro Ueda,
  • Takashi Ishiguro,
  • Ken Arimura,
  • Fukuki Saito,
  • Takashi Yoshiyama,
  • Yasushi Nakano,
  • Yoshikazu Mutoh,
  • Yusuke Suzuki,
  • Koji Murakami,
  • Yukinori Okada,
  • Ryuji Koike,
  • Yuko Kitagawa,
  • Akinori Kimura,
  • Seiya Imoto,
  • Satoru Miyano,
  • Seishi Ogawa,
  • Takanori Kanai,
  • Koichi Fukunaga,
  • The Japan COVID-19 Task Force

DOI
https://doi.org/10.1186/s12879-022-07927-w
Journal volume & issue
Vol. 22, no. 1
pp. 1 – 15

Abstract

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Abstract Background We aimed to elucidate differences in the characteristics of patients with coronavirus disease 2019 (COVID-19) requiring hospitalization in Japan, by COVID-19 waves, from conventional strains to the Delta variant. Methods We used secondary data from a database and performed a retrospective cohort study that included 3261 patients aged ≥ 18 years enrolled from 78 hospitals that participated in the Japan COVID-19 Task Force between February 2020 and September 2021. Results Patients hospitalized during the second (mean age, 53.2 years [standard deviation {SD}, ± 18.9]) and fifth (mean age, 50.7 years [SD ± 13.9]) COVID-19 waves had a lower mean age than those hospitalized during the other COVID-19 waves. Patients hospitalized during the first COVID-19 wave had a longer hospital stay (mean, 30.3 days [SD ± 21.5], p < 0.0001), and post-hospitalization complications, such as bacterial infections (21.3%, p < 0.0001), were also noticeable. In addition, there was an increase in the use of drugs such as remdesivir/baricitinib/tocilizumab/steroids during the latter COVID-19 waves. In the fifth COVID-19 wave, patients exhibited a greater number of presenting symptoms, and a higher percentage of patients required oxygen therapy at the time of admission. However, the percentage of patients requiring invasive mechanical ventilation was the highest in the first COVID-19 wave and the mortality rate was the highest in the third COVID-19 wave. Conclusions We identified differences in clinical characteristics of hospitalized patients with COVID-19 in each COVID-19 wave up to the fifth COVID-19 wave in Japan. The fifth COVID-19 wave was associated with greater disease severity on admission, the third COVID-19 wave had the highest mortality rate, and the first COVID-19 wave had the highest percentage of patients requiring mechanical ventilation.

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