Thorax 65:645-651 doi:10.1136/thx.2010.135210
  • Respiratory infection

Risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza: United Kingdom first wave (May–September 2009)

Open AccessEditor's Choice
  1. K G Nicholson10 on behalf of the Influenza Clinical Information Network (FLU-CIN)
  1. 1Division of Epidemiology and Public Health, University of Nottingham, Nottingham, UK
  2. 2Centre for Respiratory Infections, National Heart and Lung Institute, Imperial College, London, UK
  3. 3Department of Health, Skipton House, London, UK
  4. 4Department of Respiratory Medicine, Nottingham University Hospitals NHS Trust, Nottingham, UK
  5. 5School of Reproductive and Developmental Medicine, University of Liverpool, Liverpool, UK
  6. 6Department of Infection and Immunity, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK
  7. 7Department of Critical Care, Portsmouth Hospitals NHS Trust, Portsmouth, UK
  8. 8Centre for Peri-operative Medicine and Critical Care Research, Imperial College Healthcare NHS Trust, London, UK
  9. 9Health Protection Scotland, NHS National Services, Glasgow, UK
  10. 10Infectious Diseases Unit, University Hospitals of Leicester NHS Trust, Leicester Royal Infirmary, Leicester, UK
  1. Correspondence to Professor J Nguyen-Van-Tam, Division of Epidemiology and Public Health, University of Nottingham, Clinical Sciences Building, City Hospital, Hucknall Road, Nottingham NG5 1PB, UK; jvt{at}
  1. Contributors All authors were involved with designing the study and interpreted and analysed data and contributed to the report and approved the final version. JEE trained FLU-CIN data collectors, coordinated data collection, collated the data and oversaw data entry with JSN-V-T and AH. AH analysed the data. MGS adjusted the paediatric data for age and temperature. JSN-V-T and KGN wrote the report with assistance from all co-authors and are guarantors. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of their respective employers.

  • Received 14 January 2010
  • Accepted 21 April 2010


Background During the first wave of pandemic H1N1 influenza in 2009, most cases outside North America occurred in the UK. The clinical characteristics of UK patients hospitalised with pandemic H1N1 infection and risk factors for severe outcome are described.

Methods A case note-based investigation was performed of patients admitted with confirmed pandemic H1N1 infection.

Results From 27 April to 30 September 2009, 631 cases from 55 hospitals were investigated. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically-confirmed pneumonia and a raised C-reactive protein (CRP) level (≥100 mg/l). 59% of all in-hospital deaths occurred in previously healthy people.

Conclusions Pandemic H1N1 infection causes disease requiring hospitalisation of previously fit individuals as well as those with underlying conditions. An abnormal chest x-ray or a raised CRP level, especially in patients who are recorded as obese or who have pulmonary conditions other than asthma or COPD, indicate a potentially serious outcome. These findings support the use of pandemic vaccine in pregnant women, children <5 years of age and those with chronic lung disease.


  • Funding Funding was received from the Department of Health, London and from the Scottish Government Chief Medical Officer and Public Health Directorate (funding for Scottish centre only).

  • Competing interests JSN-V-T has received funding to attend influenza related meetings, lecture and consultancy fees and research funding from several influenza antiviral drug and vaccine manufacturers and is a former employee of SmithKline Beecham plc (now GlaxoSmithKline), Roche Products Ltd and Sanofi-Pasteur MSD. PJMO is a member of the European Scientific Working Group on Influenza (ESWI) which is funded by the pharmaceutical industry. EMG and CA are employees of the Department of Health, England. WSL has received research funding from Wyeth. MGS is an advisor to the Department of Health, England. SJB has received consultancy fees from GlaxoSmithKline and Baxter. JEE has received consultancy fees from GlaxoSmithKline and performed paid work for the Department of Health, England. KGN has received H5 avian influenza vaccines from Novartis and H1N1 pandemic influenza vaccines from GlaxoSmithKline and Baxter to facilitate MRC and NIHR-funded trials. He has received consultancy fees from Novartis and GlaxoSmithKline and lecture fees from Baxter. A colleague of KGN at the University Hospitals of Leicester NHS Trust was principal investigator and recipient of research funding from Roche on antiviral resistance and from Novartis on pandemic H1N1 vaccines.

  • Ethics approval Before starting this study, FLU-CIN procedures were reviewed by the Ethics and Confidentiality Committee of the National Information Governance Board for Health and Social Care in England and approved for collection, storage and use of personal data for surveillance purposes.

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

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