Journal Article

Clinical Predictors of Influenza in Young Children: The Limitations of “Influenza-Like Illness”

Nicholas T. Conway, Zoe V. Wake, Peter C. Richmond, David W. Smith, Anthony D. Keil, Simon Williams, Heath Kelly, Dale Carcione, Paul V. Effler and Christopher C. Blyth

in Journal of the Pediatric Infectious Diseases Society

Published on behalf of Pediatric Infectious Diseases Society

Volume 2, issue 1, pages 21-29
Published in print March 2013 | ISSN: 2048-7193
Published online September 2012 | e-ISSN: 2048-7207 | DOI: http://dx.doi.org/10.1093/jpids/pis081
Clinical Predictors of Influenza in Young Children: The Limitations of “Influenza-Like Illness”

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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 659 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 (20082009; 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], 5066), 60% specificity (95% CI, 5664), 26% positive predictive value (95% CI, 2131), and 86% negative predictive value (95% CI, 8289). 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, 8695), yet lacked specificity (10%; 95% CI, 813) 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.

Keywords: Influenza, Human; Child; Preschool; Population Surveillance

Journal Article.  4111 words.  Illustrated.

Subjects: Infectious Diseases ; Immunology ; Public Health and Epidemiology ; Microbiology

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