title: Hospitalization risk of the 2009 H1N1 pandemic cases in Hong Kong.
abstract: BACKGROUND
  Reliable assessment for the severity of the 2009 H1N1 pandemic influenza is critical for evaluation of vaccination strategies for future pandemics. This study aims to estimate the age-specific hospitalization risks of the 2009 pandemic cases during the first wave in Hong Kong, by combining the findings from the serology and disease burden studies.
  
  
  METHODS
  Excess hospitalization rates associated with the pandemic H1N1 were estimated from Poisson regression models fitted to weekly total numbers of non-accidental hospitalization from 2005 to 2010. Age-specific infection-hospitalization risks were calculated as excess hospitalization rates divided by the attack rates in the corresponding age group, which were estimated from serology studies previously conducted in Hong Kong.
  
  
  RESULTS
  Excess hospitalization rate associated with pandemic H1N1 was highest in the 0-4 age group (881.3 per 100,000 population), followed by the 5-14, 60+, 15-29, 50-59, 30-39 and 40-49 age groups. The hospitalization risk of the infected cases (i.e. infection-hospitalization risk) was found highest in the 60+ age group and lowest in the 15-29 age group, with the estimates of 17.5% and 0.7%, respectively.
  
  
  CONCLUSIONS
  People aged 60 or over had a relatively high infection-hospitalization risk during the first wave of the 2009 H1N1 pandemic, despite of a low attack rate in this age group. The findings support the policy of listing older people as the priority group for pandemic vaccination.
authors.forename: Xi-Ling
authors.initials: XL
authors.lastname: Wang
authors.affiliation: School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, People's Republic of China. hrmrwcm@hku.hk.
authors.forename: Chit-Ming
authors.initials: CM
authors.lastname: Wong
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.forename: King-Pan
authors.initials: KP
authors.lastname: Chan
authors.forename: Pei-Hua
authors.initials: PH
authors.lastname: Cao
authors.forename: Js Malik
authors.initials: JM
authors.lastname: Peiris
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D058873:Pandemics / Q000706:statistics & numerical data; D012306:Risk; D055815:Young Adult