Abstract
Objectives
We assessed the performance of syndromic indicators based on Google Flu Trends (GFT) and emergency department (ED) data for the early detection and monitoring of the 2009 H1N1 pandemic waves in Manitoba.
Methods
Time-series curves for the weekly counts of laboratory-confirmed H1N1 cases in Manitoba during the 2009 pandemic were plotted against the three syndromic indicators: 1) GFT data, based on flu-related Internet search queries, 2) weekly count of all ED visits triaged as influenza-like illness (ED ILI volume), and 3) percentage of all ED visits that were triaged as an ILI (ED ILI percent). A linear regression model was fitted separately for each indicator and correlations with weekly virologic data were calculated for different lag periods for each pandemic wave.
Results
All three indicators peaked 1-2 weeks earlier than the epidemic curve of laboratory-confirmed cases. For GFT data, the best-fitting model had about a 2-week lag period in relation to the epidemic curve. Similarly, the best-fitting models for both ED indicators were observed for a time lag of 1-2 weeks. All three indicators performed better as predictors of the virologic time trends during the second wave as compared to the first. There was strong congruence between the time series of the GFT and both the ED ILI volume and the ED ILI percent indicators.
Conclusion
During an influenza season characterized by high levels of disease activity, GFT and ED indicators provided a good indication of weekly counts of laboratory-confirmed influenza cases in Manitoba 1-2 weeks in advance.
Key words: Epidemiology; influenza A virus, H1N1 subtype; public health surveillance
Résumé
Objectifs
Nous avons évalué l’efficacité des indicateurs syndromiques, d’après les données de Google Flu Trends (GFT) et des services d’urgence, pour le dépistage précoce et la surveillance des vagues de la pandémie de grippe H1N1 en 2009 au Manitoba.
Méthode
Des courbes de série chronologique des numérations hebdomadaires des cas de grippe H1N1 confirmés en laboratoire au Manitoba durant la pandémie de 2009 ont été tracées en fonction de trois indicateurs syndromiques: 1) les données de GFT, basées sur les recherches liées à la grippe lancées sur Internet, 2) les visites aux urgences de catégorie « syndrome grippal » en nombres hebdomadaires (volume de SG aux urgences) et 3) les mêmes visites, mais en pourcentage (pourcentage de SG aux urgences). Un modèle de régression linéaire a été assorti séparément à chaque indicateur, et les corrélations avec les données virologiques hebdomadaires ont été calculées pour les différentes périodes de latence de chaque vague pandémique.
Résultats
Les trois indicateurs ont atteint un sommet 1 à 2 semaines plus tôt que la courbe épidémique des cas confirmés en laboratoire. Pour les données de GFT, le modèle le mieux assorti présentait une période de latence d’environ 2 semaines par rapport à la courbe épidémique. De même, les modèles les mieux assortis pour les deux indicateurs des urgences présentaient une période de latence d’1 à 2 semaines. Les trois indicateurs ont mieux fonctionné comme variables prédictives des tendances virologiques dans le temps durant la seconde vague que durant la première. Il y avait une forte concordance entre la série chronologique de GFT et les indicateurs de volume et de pourcentage de SG aux urgences.
Conclusion
Durant une saison grippale caractérisée par de hauts niveaux d’activité de la maladie, les indicateurs de GFT et des services d’urgence ont donné une bonne indication des numérations hebdomadaires des cas de grippe confirmés en laboratoire au Manitoba avec 1 à 2 semaines d’avance.
Mots clés: épidémiologie, virus A de la grippe sous-type H1N1, surveillance de santé, publique
Footnotes
Financial support: This work was partially supported by CIHR Pandemic Outbreak Team Leader Grant (PTL-97126).
Disclaimer: The interpretation and conclusions contained herein do not necessarily represent those of the Winnipeg Regional Health Authority.
Conflict of Interest: None to declare.
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