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Open Access Highly Accessed Research article

Evaluation of the seroprevalence of influenza A(H1N1) 2009 on a university campus: a cross-sectional study

Shira C Shafir12*, Kaitlin A O'Keefe2 and Kimberley I Shoaf13

Author Affiliations

1 Center for Public Health and Disasters, School of Public Health, University of California, Los Angeles, CA, USA

2 Department of Epidemiology, School of Public Health, University of California, Los Angeles, CA, USA

3 Department of Community Health Sciences, School of Public Health, University of California, Los Angeles, CA, USA

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BMC Public Health 2011, 11:922  doi:10.1186/1471-2458-11-922

Published: 13 December 2011

Abstract

Background

Human infection with influenza A(H1N1) 2009 was first identified in the United States on 15 April 2009 and on 11 June 2009, WHO declared that the rapidly spreading swine-origin influenza virus constituted a global pandemic. We evaluated the seroprevalence of influenza A(H1N1) 2009 virus on a large public University campus, as well as disparities in demographic, symptomatic and vaccination characteristics of participants.

Methods

Using a cross-sectional study design, sera was collected from volunteers and then tested for the presence of antibodies to the virus using a ≥ 1:40 dilution cut-off by hemagglutination inhibition assay. In conjunction, participants were asked to complete a questionnaire allowing us to estimate risk factors for infection in this population, as well as distinguish artificially derived antibodies from naturally derived antibodies.

Results

300 total participants were recruited and tested. 158 (52.6%) tested positive for influenza A(H1N1) 2009 via hemagglutination inhibition assay using a ≥ 1:40 dilution cut-off. 86 people (54.4%) tested positive for H1N1 but did not report experiencing symptoms during the pandemic meeting the May 2010 CDC definition of influenza-like illness. Furthermore, of those individuals who reported that they had received the H1N1 vaccine, 16% did not test positive.

Conclusions

Overall, 52.7% of the total study population tested positive for influenza A(H1N1) 2009. 54.4% of those who tested positive for influenza A(H1N1) 2009 using the ≥ 1:40 dilution cut-off on the hemagglutination inhibition assay in this study population did not report experiencing symptoms during the pandemic meeting the May 2010 CDC definition of influenza-like illness. 16% of those who reported receiving the H1N1 vaccine did not test positive by HAI. We also found that vaccination coverage for H1N1 vaccine was poor among Blacks and Latinos, despite the fact that vaccine was readily available at no cost.