Pandemic (H1N1) 2009, New South Wales, Australia | CDC EID

Pandemic (H1N1) 2009, New South Wales, Australia | CDC EID: "EID Journal Home > Volume 17, Number 7–July 2011
Volume 17, Number 7–July 2011
Research
Epidemiology of Influenza-like Illness during Pandemic (H1N1) 2009, New South Wales, Australia

David J. Muscatello, Comments to Author Margo Barr, Sarah V. Thackway, and C. Raina MacIntyre
Author affiliations: New South Wales Department of Health, North Sydney, New South Wales, Australia (D.J. Muscatello, M. Barr, S. Thackway); University of New South Wales, Kensington, New South Wales, Australia (D.J. Muscatello, C.R. MacIntyre); and University of Wollongong, Wollongong, New South Wales, Australia (M. Barr)

Suggested citation for this article

Abstract
To rapidly describe the epidemiology of influenza-like illness (ILI) during the 2009 winter epidemic of pandemic (H1N1) 2009 virus in New South Wales, Australia, we used results of a continuous population health survey. During July–September 2009, ILI was experienced by 23% of the population. Among these persons, 51% were unable to undertake normal duties for <3 days, 55% sought care at a general practice, and 5% went to a hospital. Factors independently associated with ILI were younger age, daily smoking, and obesity. Effectiveness of prepandemic seasonal vaccine was ≈20%. The high prevalence of risk factors associated with a substantially increased risk for ILI deserves greater recognition.

During winter 2009, Australia experienced a strong influenza epidemic, caused by the pandemic (H1N1) 2009 virus. In New South Wales (NSW), the most populous state of Australia (≈7 million persons), the epidemic lasted from late June through early September (1). Despite intense surveillance and response efforts, determining the epidemiology of influenza at the whole-population level remains difficult, and considerable uncertainty about the disease remains because only a small proportion of infected persons are tested (2).

Survey methods have been infrequently used to assess the epidemiology of pandemic influenza virus infection in the general population. In 1919, a personal household interview survey using a sample of population census districts from large population centers was used to assess illness associated with the first wave of pandemic influenza in the Unites States. Persons called intelligent inspectors determined whether the household member was 'sick since September 1, 1918, with influenza, pneumonia, or indefinitely diagnosed illness suspected to be influenza.' The survey demonstrated substantial demographic, geographic, and socioeconomic variation in the apparent attack rate of influenza. Expressed as a percentage, the overall incidence rate of clinical infection was estimated to be ≈28% during the first wave. The incidence rate was ≈35% in children and declined with age to ≈30% in adults <35 years of age and to ≈10% in persons >75 years of age. Incidence was higher among women 15–35 years of age than among men in the same age group (3,4).

During the first epidemic wave of pandemic (H1N1) 2009, we used a continuous population health survey to better understand the epidemiology of the influenza (H1N1) virus in the general community. This situation also created an unprecedented opportunity to assess the prevalence of seasonal influenza vaccination among persons of all age groups in our population and its effectiveness against ILI during pandemic (H1N1) 2009.


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Suggested Citation for this Article

Muscatello DJ, Barr M, Thackway SV, MacIntyre CR. Epidemiology of influenza-like illness during pandemic (H1N1) 2009, New South Wales, Australia. Emerg Infect Dis [serial on the Internet]. 2011 Jul [date cited]. http://www.cdc.gov/EID/content/17/7/1240.htm

DOI: 10.3201/eid1707.101173

Comments to the Authors

Please use the form below to submit correspondence to the authors or contact them at the following address:

David J. Muscatello, New South Wales Department of Health, Locked Bag 961, North Sydney, NSW 2059, Australia: email: dmusc@doh.health.nsw.gov.au