Reassessing Google Flu Trends Data for Detection of Seasonal and Pandemic Influenza: A Comparative Epidemiological Study at Three Geographic Scales
Figure 1
Time-series of weekly influenza-like illness (ILI) surveillance and Google Flu Trends (GFT) search query estimates, June 2003–March 2013.
Observed weekly ILI proportions (black lines) are shown with Serfling model baseline (gray lines) and 95% epidemic threshold (dashed lines). The periods of the early wave of the 2009 pandemic and the 2012/2013 epidemic are shaded in grey. Sentinel ILI-Net surveillance is shown for (A) the United States and (B) Mid-Atlantic States (New Jersey, New York, Pennsylvania). Local ILI surveillance from emergency department visits is shown for (C) New York City. Scaled GFT internet search query estimates are shown for model-fitting periods for the original (thin red line) and updated (thin blue line) GFT models, and for the periods of prospective operation of the original (thick red line) and updated (thick blue line) GFT models. For Mid-Atlantic States the updated GFT model data represents ILI proportions only for New Jersey and New York (see Supporting Information).