Comparison of adult patients hospitalised with pandemic (H1N1) 2009 influenza and seasonal influenza during the “PROTECT” phase of the pandemic response

Ya-Shu Chang, Sebastiaan J van Hal, Peter M Spencer, Iain B Gosbell and Peter W Collett
Med J Aust 2010; 192 (2): 90-93.


Objective: To compare the patient characteristics, clinical features and outcomes of adult patients hospitalised with pandemic (H1N1) 2009 influenza and seasonal influenza.

Design and setting: Retrospective medical record review of all patients admitted to Liverpool Hospital, Sydney, with laboratory-confirmed influenza from the initiation of the “PROTECT” phase of the pandemic response on 17 June until the end of our study period on 31 July 2009.

Main outcome measures: Severity of illness; requirement for admission to the intensive care unit (ICU) and/or invasive ventilation; mortality.

Results: Sixty-four adults were admitted to Liverpool Hospital with influenza, 48 with pandemic (H1N1) 2009 influenza and 16 with seasonal influenza. Thirteen patients were admitted to the ICU. Seven required invasive ventilation, with 2 patients requiring ongoing extracorporeal membrane oxygenation (ECMO). Five patients died (mortality rate, 8%) with two deaths occurring after the study period. Patients with pandemic (H1N1) 2009 influenza were younger and less likely to be immunocompromised than patients with seasonal influenza. However, the clinical features of pandemic (H1N1) 2009 influenza and seasonal influenza were similar.

Conclusions: Our findings show that the clinical course and outcomes of pandemic (H1N1) 2009 influenza virus are comparable to those of the current circulating seasonal influenza in Sydney. The high number of hospital admissions reflects a high incidence of disease in the community rather than an enhanced virulence of the novel pandemic influenza virus.

  • Ya-Shu Chang1
  • Sebastiaan J van Hal2
  • Peter M Spencer1
  • Iain B Gosbell3,2
  • Peter W Collett1

  • 1 Department of Respiratory Medicine, Liverpool Hospital, Sydney, NSW.
  • 2 Department of Microbiology and Infectious Diseases, Sydney South West Pathology Service, Sydney, NSW.
  • 3 Microbiology and Infectious Diseases Unit, School of Medicine, University of Western Sydney, Sydney, NSW.



We thank the medical and nursing staff of Liverpool Hospital, who assisted with the clinical care of patients affected by influenza, and the scientific staff of Sydney South West Pathology Service — Liverpool, who performed the diagnostic testing on the patients. We also thank Professor Guy Marks for his comments on our manuscript.

Competing interests:

None identified.

  • 1. Ginsberg M, Hopkins J, Maroufi A, et al. Swine influenza A (H1N1) infection in two children — southern California, March–April 2009. MMWR Morb Mortal Wkly Rep 2009; 58: 400-402.
  • 2. World Health Organization. Pandemic (H1N1) 2009. (accessed 6 Aug 2009).
  • 3. Australian Government Department of Health and Ageing. Australian health management plan for pandemic influenza. 2008. (accessed 6 Aug 2009).
  • 4. Kaufman MA, Duke GJ, McGain F, et al. Life-threatening respiratory failure from H1N1 influenza 09 (human swine influenza). Med J Aust 2009; 191: 154-156. <MJA full text>
  • 5. Fonseca V, Davis M, Wing R, et al. Novel influenza A (H1N1) virus infections in three pregnant women — United States, April–May 2009. MMWR Morb Mortal Wkly Rep 2009; 58: 497-500.
  • 6. Jamieson DJ, Honein MA, Rasmussen SA, et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet 2009; 374: 451-458.
  • 7. Australian Government Department of Health and Ageing. H1N1 Influenza 09 latest news. New pandemic phase PROTECT. 17 June 2009. (accessed Nov 2009).
  • 8. New South Wales Department of Health. Emergency. Pandemic influenza A (H1N1) 2009. Questions and answers. Common questions and answers regarding H1N1 Influenza 09. (accessed 6 Aug 2009).
  • 9. Centers for Disease Control and Prevention. Influenza. In: Heymann DL, editor. Control of communicable diseases manual. Washington, DC: American Public Health Association, 2008: 315-331.
  • 10. Harris JW. Influenza occurring in pregnant women. JAMA 1919; 72: 978-980.
  • 11. Freeman DW, Barno A. Deaths from Asian influenza associated with pregnancy. Am J Obstet Gynecol 1959; 78: 1172-1175.
  • 12. Neuzil KM, Reed GW, Mitchel EF, et al. Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women. Am J Epidemiol 1998; 148: 1094-1102.
  • 13. Perez-Padilla R, de la Rosa-Zamboni D, Ponce de Leon S, et al. Pneumonia and respiratory failure from swine-origin influenza A (H1N1) in Mexico. N Engl J Med 2009; 361: 680-689. Epub 2009 Jun 29.


remove_circle_outline Delete Author
add_circle_outline Add Author

Do you have any competing interests to declare? *

I/we agree to assign copyright to the Medical Journal of Australia and agree to the Conditions of publication *
I/we agree to the Terms of use of the Medical Journal of Australia *
Email me when people comment on this article

Responses are now closed for this article.