title: Clinical Predictors of Influenza in Young Children: The Limitations of "Influenza-Like Illness".
abstract: BACKGROUND
  Influenza-like illness (ILI) definitions have been infrequently studied in young children. Despite this, clinical definitions of ILI play an important role in influenza surveillance. This study aims to identify clinical predictors of influenza infection in children ≤5 years old from which age-specific ILI definitions are then constructed.
  
  
  METHODS
  Children aged 6-59 months with a history of fever and acute respiratory symptoms were recruited in the Western Australia Influenza Vaccine Effectiveness (WAIVE) Study. Clinical data and per-nasal specimens were obtained from all children. Logistic regression identified significant predictors of influenza infection. Different ILI definitions were compared for diagnostic accuracy.
  
  
  RESULTS
  Children were recruited from 2 winter influenza seasons (2008-2009; n = 944). Of 919 eligible children, 179 (19.5%) had laboratory-confirmed influenza infection. Predictors of infection included increasing age, lack of influenza vaccination, lower birth weight, fever, cough, and absence of wheeze. An ILI definition comprising fever ≥38°C, cough, and no wheeze had 58% sensitivity (95% confidence interval [CI], 50-66), 60% specificity (95% CI, 56-64), 26% positive predictive value (95% CI, 21-31), and 86% negative predictive value (95% CI, 82-89). The addition of other symptoms or higher fever thresholds to ILI definition had little impact. The Centers for Disease Control and Prevention definition of ILI (presence of fever [≥37.8°C] and cough and/or sore throat) was sensitive (92%; 95% CI, 86-95), yet lacked specificity (10%; 95% CI, 8-13) in this population.
  
  
  CONCLUSIONS
  Influenza-like illness is a poor predictor of laboratory-confirmed influenza infection in young children but can be improved using age-specific data. Incorporating age-specific ILI definitions and/or diagnostic testing into influenza surveillance systems will improve the accuracy of epidemiological data.
authors.affiliation: Vaccine Trials Group, Telethon Institute for Child Health Research, Perth, Western Australia Child Health, University of Dundee, Scotland.
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Conway
authors.affiliation: Department of Paediatric and Adolescent Medicine, Princess Margaret Hospital for Children.
authors.forename: Zoe V
authors.initials: ZV
authors.lastname: Wake
authors.affiliation: Vaccine Trials Group, Telethon Institute for Child Health Research, Perth, Western Australia Department of Paediatric and Adolescent Medicine, Princess Margaret Hospital for Children School of Paediatrics and Child Health, University of Western Australia, Perth.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Richmond
authors.affiliation: PathWest Laboratory Medicine WA, QEII Medical Centre, Nedlands School of Pathology and Laboratory Medicine, University of Western Australia, Perth.
authors.forename: David W
authors.initials: DW
authors.lastname: Smith
authors.affiliation: Department of Microbiology, PathWest Laboratory Medicine, Princess Margaret Hospital for Children, Perth, Western Australia.
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Keil
authors.affiliation: PathWest Laboratory Medicine WA, QEII Medical Centre, Nedlands.
authors.forename: Simon
authors.initials: S
authors.lastname: Williams
authors.affiliation: Victorian Infectious Diseases Reference Laboratory, North Melbourne, Victoria, Australia.
authors.forename: Heath
authors.initials: H
authors.lastname: Kelly
authors.affiliation: Communicable Disease Control Directorate, Department of Health, Perth, Western Australia.
authors.forename: Dale
authors.initials: D
authors.lastname: Carcione
authors.affiliation: Communicable Disease Control Directorate, Department of Health, Perth, Western Australia.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Effler
authors.affiliation: Vaccine Trials Group, Telethon Institute for Child Health Research, Perth, Western Australia Department of Paediatric and Adolescent Medicine, Princess Margaret Hospital for Children School of Paediatrics and Child Health, University of Western Australia, Perth Department of Microbiology, PathWest Laboratory Medicine, Princess Margaret Hospital for Children, Perth, Western Australia.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Blyth
keywords: Child; Influenza, Human; Population Surveillance; Preschool