title: An evidence synthesis approach to estimating the incidence of seasonal influenza in the Netherlands.
abstract: OBJECTIVE
  To estimate, using Bayesian evidence synthesis, the age-group-specific annual incidence of symptomatic infection with seasonal influenza in the Netherlands over the period 2005-2007.
  
  
  METHODS
  The Netherlands population and age group distribution for 2006 defined the base population. The number of influenza-like illness (ILI) cases was estimated from sentinel surveillance data and adjusted for underascertainment using the estimated proportion of ILI cases that do not consult a general practitioner. The estimated number of symptomatic influenza (SI) cases was based on indirect evidence from the surveillance of ILI cases and the proportions of laboratory-confirmed influenza cases in the 2004/5, 2005/6 and 2006/7 respiratory years. In scenario analysis, the number of SI cases prevented by increasing vaccination uptake within the 65 +  age group was estimated.
  
  
  RESULTS
  The overall symptomatic infection attack rate (SIAR) over the period 2005-2007 was estimated at 2·5% (95% credible interval [CI]: 2·1-3·2%); 410 200 SI cases (95% CI: 338 500-518 600) were estimated to occur annually. Age-group-specific SIARs were estimated for <5 years at 4·9% (2·1-13·7%), for 5-14 years at 3·0% (2·0-4·7%), for 15-44 years at 2·6% (2·1-3·2%), for 45-64 years at 1·9% (1·4-2·5%) and for 65 +  years at 1·7% (1·0-3·0%). Under assumed vaccination uptake increases of 5% and 15%, 1970 and 5310 SI cases would be averted.
  
  
  CONCLUSIONS
  By synthesising the available information on seasonal influenza and ILI from diverse sources, the annual extent of symptomatic infection can be derived. These estimates are useful for assessing the burden of seasonal influenza and for guiding vaccination policy.
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands.
authors.forename: Scott A
authors.initials: SA
authors.lastname: McDonald
authors.forename: Anne M
authors.initials: AM
authors.lastname: Presanis
authors.forename: Daniela
authors.initials: D
authors.lastname: De Angelis
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
authors.forename: Mariette
authors.initials: M
authors.lastname: Hooiveld
authors.forename: Gé
authors.initials: G
authors.lastname: Donker
authors.forename: Mirjam E
authors.initials: ME
authors.lastname: Kretzschmar
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D055815:Young Adult
keywords: Bayesian evidence synthesis; incidence; seasonal influenza; vacciation