title: Inaccurate ascertainment of morbidity and mortality due to influenza in administrative databases: a population-based record linkage study.
abstract: BACKGROUND
  Historically, counting influenza recorded in administrative health outcome databases has been considered insufficient to estimate influenza attributable morbidity and mortality in populations. We used database record linkage to evaluate whether modern databases have similar limitations.
  
  
  METHODS
  Person-level records were linked across databases of laboratory notified influenza, emergency department (ED) presentations, hospital admissions and death registrations, from the population (∼6.9 million) of New South Wales (NSW), Australia, 2005 to 2008.
  
  
  RESULTS
  There were 2568 virologically diagnosed influenza infections notified. Among those, 25% of 40 who died, 49% of 1451 with a hospital admission and 7% of 1742 with an ED presentation had influenza recorded on the respective database record. Compared with persons aged ≥65 years and residents of regional and remote areas, respectively, children and residents of major cities were more likely to have influenza coded on their admission record. Compared with older persons and admitted patients, respectively, working age persons and non-admitted persons were more likely to have influenza coded on their ED record. On both ED and admission records, persons with influenza type A infection were more likely than those with type B infection to have influenza coded. Among death registrations, hospital admissions and ED presentations with influenza recorded as a cause of illness, 15%, 28% and 1.4%, respectively, also had laboratory notified influenza. Time trends in counts of influenza recorded on the ED, admission and death databases reflected the trend in counts of virologically diagnosed influenza.
  
  
  CONCLUSIONS
  A minority of the death, hospital admission and ED records for persons with a virologically diagnosed influenza infection identified influenza as a cause of illness. Few database records with influenza recorded as a cause had laboratory confirmation. The databases have limited value for estimating incidence of influenza outcomes, but can be used for monitoring variation in incidence over time.
authors.affiliation: Centre for Epidemiology and Evidence, New South Wales Ministry of Health, North Sydney, W, Australia; School of Public Health and Community Medicine, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: David J
authors.initials: DJ
authors.lastname: Muscatello
authors.affiliation: The Kirby Institute, The University of New South Wales, Coogee, New South Wales, Australia.
authors.forename: Janaki
authors.initials: J
authors.lastname: Amin
authors.affiliation: School of Public Health and Community Medicine, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: C Raina
authors.initials: CR
authors.lastname: MacIntyre
authors.affiliation: School of Public Health and Community Medicine, The University of New South Wales, Kensington, New South Wales, Australia.
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Newall
authors.affiliation: South East Area Laboratory Service, The Prince of Wales Hospital, Randwick, New South Wales, Australia; Faculty of Medicine, The University of New South Wales, New South Wales, Australia.
authors.forename: William D
authors.initials: WD
authors.lastname: Rawlinson
authors.affiliation: Sydney Medical School, The University of Sydney, Camperdown, New South Wales, Australia; Centre for Infectious Diseases and Microbiology, Pathology West - Institute for Clinical Pathology and Medical Research, Westmead, New South Wales, Australia.
authors.forename: Vitali
authors.initials: V
authors.lastname: Sintchenko
authors.affiliation: Centre for Epidemiology and Evidence, New South Wales Ministry of Health, North Sydney, W, Australia.
authors.forename: Robin
authors.initials: R
authors.lastname: Gilmour
authors.affiliation: Centre for Epidemiology and Evidence, New South Wales Ministry of Health, North Sydney, W, Australia.
authors.forename: Sarah
authors.initials: S
authors.lastname: Thackway
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D016208:Databases, Factual; D018563:Disease Notification; D005260:Female; D006760:Hospitalization; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D009017:Morbidity; D009026:Mortality; D009517:New South Wales / Q000453:epidemiology; D011159:Population Surveillance; D015203:Reproducibility of Results; D055815:Young Adult