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Incidence of hospitalisation for severe complications of influenza virus infection in Japanese patients between 2012 and 2016: a cross-sectional study using routinely collected administrative data
  1. Hiroshi Yokomichi1,
  2. Mie Mochizuki2,
  3. Joseph Jonathan Lee3,
  4. Reiji Kojima1,
  5. Tetsuji Yokoyama4,
  6. Zentaro Yamagata1
  1. 1 Department of Health Sciences, University of Yamanashi, Chuo City, Japan
  2. 2 Department of Pediatrics, University of Yamanashi, Chuo City, Japan
  3. 3 Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK
  4. 4 Department of Health Promotion, National Institute of Public Health, Wako City, Japan
  1. Correspondence to Dr Hiroshi Yokomichi; hyokomichi{at}


Objective To calculate the incidence of hospitalisation due to acute respiratory failure, pneumonia, acute respiratory distress syndrome (ARDS), febrile seizures and encephalitis/encephalopathy among influenza-positive patients in Japan, where point-of-care tests are routinely used to diagnose influenza.

Design A cross-sectional study using routinely collected data.

Setting Japanese clinics and hospitals between 2012 and 2016.

Participants Japanese patients aged 0–74 years diagnosed with influenza by a rapid test in employment-related health insurance records.

Primary outcome measures Incidence of hospitalisation per 100 000 influenza-positive episodes.

Results We included over 16 million influenza-positive episodes, 1.0% of whom were hospitalised. Of these, 3361 were acute respiratory failure, 27 253 pneumonia, 18 ARDS, 2603 febrile seizure and 159 encephalitis/encephalopathy. The percentage of hospitalisations by age was 2.96% of patients aged 0–1 years, 0.77% aged 2–5, 0.51% aged 6–12, 0.78% aged 13–18, 1.36% aged 19–44, 1.19% aged 45–64, and 2.21% aged 65–74. The incidence of hospitalisations from these five complications combined was highest in influenza-positive patients aged 0–1 years (943 per 100 000) compared with 307 in those aged 2–5 years and 271 in those aged 65–74 years. For pneumonia, the incidence was highest for influenza-positive patients aged 0–5 years and 65 years or more. There were statistically significant decreasing trends over the years in the incidence of all-cause hospitalisations, pneumonia and febrile seizures.

Conclusions Japanese administrative data revealed that 1.0% of influenza-positive patients aged under 75 years were hospitalised. Male patients had a higher incidence of pulmonary complications and febrile seizures. Children aged 0–5 years and adults aged 65–74 years were at high risk of being admitted to hospital for pneumonia.

  • influenza
  • hospitalisation
  • pneumonia
  • influenza encephalopathy
  • influenza encephalitis
  • febrile seizure

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  • Patient consent for publication Not required.

  • Contributors All of the authors agreed with the manuscript’s results and conclusion and approved the final version of the manuscript. HY conceived the study. HY, MM, JJL, RK, TY and ZY contributed to the design of the study and interpretation of the data analyses. HY analysed the data. HY, JJL, MM and RK wrote the first draft of the manuscript. JJL, RK, MM, ZY and HY contributed to revision of the manuscript. ZY and HY were responsible for data integrity. HY obtained funding.

  • Funding This work was supported by funding from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) (KAKENHI grant numbers JP15K08730 and JP18K17376).

  • Competing interests None declared.

  • Ethics approval The ethics committee of the School of Medicine, University of Yamanashi approved this study (approval number: H29-1709), in accordance with the ethical guidelines and regulations of the Declaration of Helsinki. The data were properly anonymised by the JMDC in the manner permitted by Japanese guideline of Personal Information Protection Commission, Cabinet Office, Government of Japan for the use of data from medical examinations in medical research without individual participants' consent (Act on the Protection of Personal Information, Act No 57 of 30 May 2003; last version amendment of Act No 65 of 2015).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The original administrative data are available through a formal request to the JMDC, subject to fees.

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