Short communicationViral genetic sequence variations in pandemic H1N1/2009 and seasonal H3N2 influenza viruses within an individual, a household and a community
Section snippets
Background
The emergence of pandemic H1N1/2009 virus provided an unique opportunity to study the dynamics of influenza virus transmission in humans1, 2 and comparative studies of pandemic and seasonal viruses within households may provide important understanding in this regard.3 We previously conducted a prospective household transmission study and concluded that pandemic and seasonal viruses have broadly similar viral-load dynamics, disease severities, and transmissibilities in the household setting.4
Objectives
The aim of this study is to elucidate the genetic sequence variation in HA and NA virus gene segments in these sequential specimens from index cases and secondary cases of infection. In addition, the epidemiological links of these household samples were also studied.
Study design
Three hundred forty-eight index patients with acute respiratory illness from a local network of 14 outpatient clinics were recruited from June to August 2009. We followed the household contacts of 99 index patients who tested positive for influenza A virus on rapid diagnostic testing in an outpatient setting and collected nasal and throat swabs (NTS) from these index cases as well as all household members regardless of illness at three subsequent home visits within 7 days. NTS were sampled and
Results and discussion
A total of 119 influenza viruses were isolated from 98 individuals in 78 households (pandemic H1N1 (pH1N1) = 61; seasonal H1N1 (sH1N1) = 4; seasonal H3N2 (sH3N2) = 54). Of these 119 viral isolates, 42 were sampled from 21 individuals (pH1N1 = 14; sH3N2 = 7) who were positive in two consecutive visits. Twenty pH1N1 and 15 sH3N2 viruses were isolated from households with confirmed secondary transmission (pH1N1 = 8; sH3N2 = 8). On one occasion, a pH1N1 and a sH3N2 viruses were isolated from different members of
Conclusion
Our results demonstrated that there were multiple introductions of pH1N1 and sH3N2 viruses into Hong Kong in 2009. Although multiple clades of pH1N1 and sH3N2 viruses co-circulated at the community level, viruses isolated from the same household were usually derived from the same viral lineage. Natural sequence variations could be detected in some sequential samples from the same person and also within the same household, suggesting influenza viral sequence variations might be more dynamic that
Funding
This study was supported by the Area of Excellence Scheme of the University Grants Committee Hong Kong (AoE/M-12/06), the Research Fund for the Control of Infectious Disease Commissioned Project from Food and Health Bureau, the NIH (NIAID contracts HHS-N266200700005C and N01-AI-70005), and the Harvard Center for Communicable Disease Dynamics from the National Institute of General Medical Sciences (grant number U54 GM088558). The funding bodies were not involved in the collection, analysis and
Conflict of interest
The authors have no commercial or other associations that may pose a conflict of interest.
Ethical approval
The procedures described in this study was reviewed and approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (Ref Number: UW 06-350T/1375).
Acknowledgements
We thank Chan Kit Man, Rita Fung, Lai-Ming Ho, Ho Yuk Ling, Lam Yiu Pong, Lincoln Lau, Tom Lui, Tong Hok Leung, Loretta Mak, Gloria Ng, Teresa So, Alfred Yeung, Eileen Yeung and Jenny Yuen for research support.
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