Abstract
Objective
Several surveillance definitions of influenza-like illness (ILI) have been proposed, based on the presence of symptoms. Symptom data can be obtained from patients, medical records, or both. Past research has found that agreements between health record data and self-report are variable depending on the specific symptom. Therefore, we aimed to explore the implications of using data on influenza symptoms extracted from medical records, similar data collected prospectively from outpatients, and the combined data from both sources as predictors of laboratory-confirmed influenza.
Methods
Using data from the Hutterite Influenza Prevention Study, we calculated: 1) the sensitivity, specificity and predictive values of individual symptoms within surveillance definitions; 2) how frequently surveillance definitions correlated to laboratory-confirmed influenza; and 3) the predictive value of surveillance definitions.
Results
Of the 176 participants with reports from participants and medical records, 142 (81%) were tested for influenza and 37 (26%) were PCR positive for influenza. Fever (alone) and fever combined with cough and/or sore throat were highly correlated with being PCR positive for influenza for all data sources. ILI surveillance definitions, based on symptom data from medical records only or from both medical records and self-report, were better predictors of laboratory-confirmed influenza with higher odds ratios and positive predictive values.
Discussion
The choice of data source to determine ILI will depend on the patient population, outcome of interest, availability of data source, and use for clinical decision making, research, or surveillance.
Keywords: Influenza, influenza-like illness, surveillance definition, data source
Résumé
Objectif
Plusieurs définitions du syndrome grippal (SG) à des fins de surveillance ont été proposées, d’après la présence de symptômes. Les données sur les symptômes peuvent être obtenues auprès des patients, dans les dossiers médicaux ou les deux. Les recherches passées ont montré que la concordance entre les données des dossiers médicaux et les données autodéclarées est variable, selon le symptôme à l’étude. Nou avons donc voulu explorer la validité d’utiliser des données sur les symptômes de la grippe extraites des dossiers médicaux, des données semblables recueillies prospectivement auprès de malades ambulatoires et des données combinant ces deux sources comme variables prédictives de la grippe confirmée en laboratoire.
Méthode
À l’aide des données d’une étude sur la prévention de la grippe dans la communauté huttérienne, nous avons calculé: 1) la sensibilité, la spécificité et la valeur prédictive de chaque symptôme compris dans les définitions à des fins de surveillance; 2) la fréquence à laquelle ces définitions étaient corrélées à la grippe confirmée en laboratoire; et 3) la valeur prédictive de ces définitions.
Résultats
Des 176 participants pour lesquels nous avions des données autodéclarées et des dossiers médicaux, 142 (81%) ont été dépistés pour la grippe et 37 (26%) ont obtenu un résultat positif à l’épreuve de détection de la grippe par la méthode PCR. Pour toutes les sources de données, la fièvre (seule) et la fièvre combinée à la toux et/ou au mal de gorge étaient hautement corrélées à une épreuve RPC positive pour la grippe. Les définitions du SG à des fins de surveillance fondées sur les symptômes indiqués dans le dossier médical seulement, ou à la fois dans le dossier médical et la déclaration du patient, étaient de meilleures variables prédictives de la grippe confirmée en laboratoire (rapports de cotes et valeurs prédictives positives plus élevés).
Discussion
Le choix de la source de données pour déterminer le SG dépend de la population de patients, du résultat attendu, de la disponibilité des sources de données et de l’utilisation des données pour la prise de décisions cliniques, la recherche ou la surveillance.
Mots clés: grippe, syndrome grippal, surveillance (définition), source de données
Footnotes
Conflict of Interest: None to declare.
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