Impact of the 2009 H1N1 Pandemic on Age-Specific Epidemic Curves of Other Respiratory Viruses: A Comparison of Pre-Pandemic, Pandemic and Post-Pandemic Periods in a Subtropical City

Lin Yang; Kwok Hung Chan; Lorna K P Suen; King Pan Chan; Xiling Wang; Peihua Cao; Daihai He; J S Malik Peiris; Chit Ming Wong

doi:10.1371/journal.pone.0125447

Impact of the 2009 H1N1 Pandemic on Age-Specific Epidemic Curves of Other Respiratory Viruses: A Comparison of Pre-Pandemic, Pandemic and Post-Pandemic Periods in a Subtropical City

PLoS One. 2015 Apr 30;10(4):e0125447. doi: 10.1371/journal.pone.0125447. eCollection 2015.

Authors

Lin Yang¹, Kwok Hung Chan², Lorna K P Suen¹, King Pan Chan³, Xiling Wang³, Peihua Cao³, Daihai He⁴, J S Malik Peiris⁵, Chit Ming Wong³

Affiliations

¹ School of Nursing, The Hong Kong Polytechnic University, Hong Kong.
² Department of Microbiology, The University of Hong Kong, Hong Kong.
³ Division of Epidemiology and Biostatistics, School of Public Health, The University of Hong Kong, Hong Kong.
⁴ Department of Applied Mathematics, The Hong Kong Polytechnic University, Hong Kong.
⁵ State Key Laboratory of Emerging Infectious Disease, School of Public Health, The University of Hong Kong, Hong Kong.

Abstract

Background: The 2009 H1N1 influenza pandemic caused offseason peaks in temperate regions but coincided with the summer epidemic of seasonal influenza and other common respiratory viruses in subtropical Hong Kong. This study was aimed to investigate the impact of the pandemic on age-specific epidemic curves of other respiratory viruses.

Methods: Weekly laboratory-confirmed cases of influenza A (subtypes seasonal A(H1N1), A(H3N2), pandemic virus A(H1N1)pdm09), influenza B, respiratory syncytial virus (RSV), adenovirus and parainfluenza were obtained from 2004 to 2013. Age-specific epidemic curves of viruses other than A(H1N1)pdm09 were compared between the pre-pandemic (May 2004-April 2009), pandemic (May 2009-April 2010) and post-pandemic periods (May 2010-April 2013).

Results: There were two peaks of A(H1N1)pdm09 in Hong Kong, the first in September 2009 and the second in February 2011. The infection rate was found highest in young children in both waves, but markedly fewer cases in school children were recorded in the second wave than in the first wave. Positive proportions of viruses other than A(H1N1)pdm09 markedly decreased in all age groups during the first pandemic wave. After the first wave of the pandemic, the positive proportion of A(H3N2) increased, but those of B and RSV remained slightly lower than their pre-pandemic proportions. Changes in seasonal pattern and epidemic peak time were also observed, but inconsistent across virus-age groups.

Conclusion: Our findings provide some evidence that age distribution, seasonal pattern and peak time of other respiratory viruses have changed since the pandemic. These changes could be the result of immune interference and changing health seeking behavior, but the mechanism behind still needs further investigations.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Adolescent
Adult
Age Distribution
Aged
Child
Child, Preschool
Female
Hong Kong / epidemiology
Humans
Infant
Infant, Newborn
Influenza A Virus, H1N1 Subtype / genetics*
Influenza A Virus, H1N1 Subtype / pathogenicity
Influenza A Virus, H3N2 Subtype / genetics*
Influenza A Virus, H3N2 Subtype / pathogenicity
Influenza, Human / epidemiology
Influenza, Human / virology*
Male
Middle Aged
Young Adult

Grants and funding

This work was supported by the Health and Medical Research Fund (grants 11100582 and 12111232) and the Area of Excellence Scheme of the University Grants Committee (grant AoE/M-12/-06) of the Hong Kong Special Administrative Region Government. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.