Comparative epidemiology of pandemic and seasonal influenza A in households.
BACKGROUND
There are few data on the comparative epidemiology and virology of the pandemic 2009 influenza A (H1N1) virus and cocirculating seasonal influenza A viruses in community settings.


METHODS
We recruited 348 index patients with acute respiratory illness from 14 outpatient clinics in Hong Kong in July and August 2009. We then prospectively followed household members of 99 patients who tested positive for influenza A virus on rapid diagnostic testing. We collected nasal and throat swabs from all household members at three home visits within 7 days for testing by means of quantitative reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assay and viral culture. Using hemagglutination-inhibition and viral-neutralization assays, we tested baseline and convalescent serum samples from a subgroup of patients for antibody responses to the pandemic and seasonal influenza A viruses.


RESULTS
Secondary attack rates (as confirmed on RT-PCR assay) among household contacts of index patients were similar for the pandemic influenza virus (8%; 95% confidence interval [CI], 3 to 14) and seasonal influenza viruses (9%; 95% CI, 5 to 15). The patterns of viral shedding and the course of illness among index patients were also similar for the pandemic and seasonal influenza viruses. In a subgroup of patients for whom baseline and convalescent serum samples were available, 36% of household contacts who had serologic evidence of pandemic influenza virus infection did not shed detectable virus or report illness.


CONCLUSIONS
Pandemic 2009 H1N1 virus has characteristics that are broadly similar to those of seasonal influenza A viruses in terms of rates of viral shedding, clinical illness, and transmissibility in the household setting.
Cowling
Benjamin J
BJ
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Chan
Kwok Hung
KH
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Fang
Vicky J
VJ
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Lau
Lincoln L H
LLH
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
So
Hau Chi
HC
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Fung
Rita O P
ROP
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Ma
Edward S K
ESK
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Kwong
Alfred S K
ASK
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Chan
Chi-Wai
CW
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Tsui
Wendy W S
WWS
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Ngai
Ho-Yin
HY
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Chu
Daniel W S
DWS
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Lee
Paco W Y
PWY
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Chiu
Ming-Chee
MC
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Leung
Gabriel M
GM
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
Peiris
Joseph S M
JSM
Infectious Disease Epidemiology Group, School of Public Health (B.J.C., V.J.F., L.L.H.L., H.C.S., R.O.P.F., G.M.L.), and the Department of Microbiology (K.H.C., E.S.K.M., J.S.M.P.), Li Ka Shing Faculty of Medicine, University of Hong Kong; Hospital Authority, Government of the Hong Kong Special Administrative Region (A.S.K.K., C.-W.C., W.W.S.T., H.-Y.N., D.W.S.C.); St. Paul's Hospital (P.W.Y.L.); St. Teresa's Hospital (M.-C.C.); and HKU-Pasteur Research Centre (J.S.M.P.) - all in Hong Kong.
D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D018562:Disease Transmission, Infectious / Q000706:statistics & numerical data; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission / Q000821:virology; D008297:Male; D008875:Middle Aged; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017201:Virus Shedding; D055815:Young Adult
D000914:Antibodies, Viral