- The median age of patients with pandemic influenza H1N1 2009 infection was reported as 20–25 years in initial case series from Europe and the United States. This has been lowered to 13 years in the US after testing of more patients, but this may reflect differential increased testing of school-aged children as part of the pandemic response.
The median age of patients with seasonal influenza A(H1N1) infection identified through sentinel surveillance in Western Australia and Victoria in 2007–2008 was 18 and 22 years, respectively. For pandemic influenza H1N1 2009 infection, the median age of the first 244 patients identified in WA was 22 years, and median age of the first 135 patients identified through sentinel surveillance in Victoria was 21 years.
Other comparisons of the epidemiological features of pandemic and seasonal influenza are difficult because much less laboratory testing is done for seasonal than for pandemic influenza.
While early surveillance data indicated co-circulation of both pandemic and seasonal strains in WA and Victoria, more recent data from both states indicate an increasing predominance of pandemic influenza.
If the evolving pandemic allows, we should take advantage of the increased testing being conducted for pandemic influenza to learn more about the real impact of laboratory-confirmed seasonal influenza.
- 1. Senanayake SN. Swine flu update: bringing home the bacon. Med J Aust 2009; 191: 138-140 [Published online ahead of print, 17 Jun 2009] <eMJA full text>.
- 2. Kelly H, Grant K, Williams S, Smith D. H1N1 swine origin influenza infection in the United States and Europe in 2009 may be similar to H1N1 seasonal influenza infection in two Australian states in 2007 and 2008. Influenza Other Respi Viruses 2009; 3: 183-188. Epub 2009 Jun 8.
- 3. Khiabanian H, Farrell GM, St George K, Rabadan R. Differences in patient age distribution between influenza A subtypes. 30 May 2009. Columbia University Libraries Academic Commons. http://app.cul.columbia.edu:8080/ac/handle/10022/AC:P:29810 (accessed Jul 2009).
- 4. Dawood FS, Jain S, Finelli L, et al; Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med 2009; 360: 2605-2615. Epub 2009 May 7.
- 5. Surveillance Group for New Influenza A(H1N1) Virus Investigation and Control in Spain. New influenza A(H1N1) virus infections in Spain, April–May 2009. Euro Surveill 2009; 14 (19): pii=19209.
- 6. Longini IM Jr, Koopman JS, Monto AS, Fox JP. Estimating household and community transmission parameters for influenza. Am J Epidemiol 1982; 115: 736-751.
- 7. Newall AT, Kelly H, Harsley S, Scuffham PA. Cost-effectiveness of influenza vaccination in older adults: a critical review of economic evaluations targeting the 50–64 year age group. Pharmacoeconomics 2009. In press.
- 8. Newall AT, Scuffham PA. Influenza-related disease: the cost to the Australian healthcare system. Vaccine 2008; 26: 6818-6823.
- 9. Fleming DM, Zambon M, Bartelds AI, de Jong JC. The duration and magnitude of influenza epidemics: a study of surveillance data from sentinel general practices in England, Wales and the Netherlands. Eur J Epidemiol 1999; 15: 467-473.
- 10. Simonsen L. The global impact of influenza on morbidity and mortality. Vaccine 1999; 17 Suppl 1: S3-S10.
- 11. Newall AT, Wood JG, Macintyre CR. Influenza-related hospitalisation and death in Australians aged 50 years and older. Vaccine 2008; 26: 2135-2141.
- 12. Chowell G, Bertozzi SM, Colchero MA, et al. Severe respiratory disease concurrent with the circulation of H1N1 influenza. N Engl J Med 2009 Jun 29. [Epub ahead of print.]
- 13. Victorian Infectious Diseases Reference Laboratory. Sentinel influenza surveillance. http://www.vidrl.org.au/surveillance/flu%20reports/flu_idx.html (accessed Jul 2009).
- 14. Communicable Disease Control Directorate, Government of Western Australia Department of Health. Virus Watch. http://www.public.health.wa.gov.au/3/487/3/virus_watch_homepage.pm (accessed Jul 2009).
- 15. Simonsen L, Taylor RJ, Viboud C, et al. Mortality benefits of influenza vaccination in elderly people: an ongoing controversy. Lancet Infect Dis 2007; 7: 658-666.
- 16. Kelly H, Newall AT. Mortality benefits of influenza vaccination in elderly people. Lancet Infect Dis 2008; 8: 462-463; author reply 463-465.
Publication of your online response is subject to the Medical Journal of Australia's editorial discretion. You will be notified by email within five working days should your response be accepted.