RESEARCH ARTICLE


The Epidemiology of the First Wave of H1N1 Influenza Pandemic in Aus-tralia: A Population-Based Study



Julie A. Pasco1, 2, *, Geoff C. Nicholson3, Sharon L. Brennan1, 2, Kathy E. Bennett1, Amelia G. Dobbins1, Eugene Athan4
1 School of Medicine, Deakin University, Geelong, VIC 3220, Australia
1 North West Academic Centre, Department of Medicine, The University of Melbourne, St Albans, VIC 3021, Australia
1 Rural Clinical School, School of Medicine, The University of Queensland, Toowoomba, QLD 4350, Australia
1 Department of Infectious Diseases, Barwon Health Geelong, VIC 3220, Australia

Article Information


Identifiers and Pagination:

Year: 2012
Volume: 5
First Page: 80
Last Page: 85
Publisher ID: TOPHJ-5-80
DOI: 10.2174/1874944501205010080

Article History:

Received Date: 22/09/2012
Revision Received Date: 11/11/2012
Acceptance Date: 15/11/2012
Electronic publication date: 28/12/2012
Collection year: 2012

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Creative Commons License
Pasco et al.; Licensee Bentham Open

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Barwon Epidemiology and Biostatistics Unit, School of Medicine, Deakin University, PO Box 281, Geelong, Victoria 3220, Australia; Tel: +61 3 42153331; Fax: +61 3 42153491;; E-mail: juliep@barwonhealth.org.au


Abstract

Objectives:

Following the recent H1N1 influenza pandemic we were able to describe seropositivity in a repre-sentative sample of adults prior to the availability of a specific vaccine.

Methods:

This cross-sectional serological study is set in the Barwon Statistical Division, Australia. Blood samples were collected from September 2009 through to May 2010, from 1184 individuals (569 men, 615 women; median age 61.7 years), randomly selected from electoral rolls. Serum was analysed for specific H1N1 immunity using a haemagglutina-tion inhibition test. A self-report provided information about symptoms, demographics and healthcare. Associations be-tween H1N1 infection, gender, households and occupation were determined using logistic regression, adjusting for age.

Results:

Of 1184 individuals, 129 (58 men, 71 women) were seropositive. Gender-adjusted age-specific prevalence was: 8.3% 20-29 years, 13.5% 30-39, 10.4% 40-49, 6.5% 50-59, 9.7% 60-69, 10.3% 70-79, 18.8% 80+. Standardised preva-lence was 10.3% (95%CI 9.6-11.0). No associations were detected between seropositivity and gender (OR=0.82, 95%CI 0.57-1.19) or being a healthcare worker (OR=1.43, 95%CI 0.62-3.29). Smokers (OR=1.86, 95%CI 1.09-3.15) and those socioeconomically disadvantaged (OR=2.52, 95%CI 1.24-5.13) were at increased risk. Among 129 seropositive individu-als, 31 reported symptoms that were either mild (n = 13) or moderate (time off work, doctor visit, n = 18). For age <60, 39.6% of seropositive individuals reported symptoms, whereas the proportion was 13.2% for age 60+.

Conclusions:

Following the pandemic, the proportion of seropositive adults was low, but significant subclinical infection was found. Social disadvantage increased the likelihood of infection. The low symptom rate for older ages may relate to pre-existing immunity.

Keywords: Epidemiology, H1N1, hospitalization, influenza A virus, pandemics, signs and symptoms, population-based study.