title: Estimating the contribution of influenza to hospitalisations in New Zealand from 1994 to 2008.
abstract: BACKGROUND
  Influenza has a substantially but poorly measured impact on population health. Estimating its true contribution to hospitalisations remains a challenge.
  
  
  METHODS
  We used simple and comprehensive negative binomial regression models with weekly counts of hospitalisations and isolates of influenza A, B and respiratory syncytial virus for the period 1994- 2008.
  
  
  RESULTS
  The estimated annual national average number of hospitalisations attributable to influenza was 822.1(95% CI: 815.3, 828.9) for pneumonia and influenza, 1861.3 (95% CI: 1842.9, 1879.7) for respiratory illness, 12.1 (95% CI: 2.6, 21.6) for circulatory illness, 2260.0 (95% CI: 2212.2, 2307.8) for all medical illness and 2419.9 (95% CI: 2356.4, 2483.4) for all causes. The contribution of influenza to total hospitalisations was about nine times larger than indicated by routine discharge data. New Zealanders 80 years of age and older had the highest annual excess rates of influenza-related hospitalisations (327.8 per 100,000); followed by infants under 1 year (244.5 per 100,000). Estimated influenza hospitalisation rates were also markedly higher in Pacific (83.3 per 100,000) and Māori (80.0 per 100,000) compared with European/Others (58.1 per 100,000). Respiratory illness was the major contributor to all cause hospitalisations attributed to influenza accounting for 77%. Influenza hospitalisations included only a negligible contribution from circulatory illness.
  
  
  CONCLUSIONS
  These findings support efforts to reduce the impact of influenza, particularly for the most vulnerable population groups highlighted here. Analysis of the cost-effectiveness of such interventions needs to consider these higher modelled estimates of disease impact.
authors.affiliation: Department of Public Health, University of Otago, Wellington, New Zealand; Health Environment Management Agency, Ministry of Health of Vietnam, Hanoi, Viet Nam. Electronic address: khith138@student.otago.ac.nz.
authors.forename: Trang Q T
authors.initials: TQ
authors.lastname: Khieu
authors.affiliation: Department of Public Health, University of Otago, Wellington, New Zealand.
authors.forename: Nevil
authors.initials: N
authors.lastname: Pierse
authors.affiliation: Department of Public Health, University of Otago, Wellington, New Zealand.
authors.forename: Lucy Frances
authors.initials: LF
authors.lastname: Telfar-Barnard
authors.affiliation: WHO National Influenza Centre, Institute of Environmental Science & Research, Wellington, New Zealand.
authors.forename: Q Sue
authors.initials: QS
authors.lastname: Huang
authors.affiliation: Department of Public Health, University of Otago, Wellington, New Zealand.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Baker
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human; D008297:Male; D008875:Middle Aged; D009520:New Zealand / Q000453:epidemiology; D055815:Young Adult
keywords: Hospitalisation; Influenza; Regression model; Virus