Objective
To test if Google Flu Trends (GFT) is predictive of the volume of influenza and pneumonia emergency department (ED) visits across multiple United States cities.
Introduction
GFT is a surveillance tool that gathers data on local internet searches to estimate the emergence of influenza-like illness in a given geographic location in real time [3]. Previously, GFT has been proven to strongly correlate with influenza incidence at the national and regional level [2,3]. GFT has shown promise as an easily accessed tool to enhance influenza surveillance and forecasting; however, further geographic validation of city-level data is needed [1,2,6].
Methods
Using Healthcare Cost and Utilization Project (HCUP) data, we collected weekly counts of ED visits for all patients with ICD-9 codes for pneumonia or influenza from 2005-2011 at 19 different cities geographically spread throughout the US [5]. Corresponding GFT data for cities and associated states were collected [4]. We then evaluated the correlation between GFT and the volume of pneumonia and influenza-related ED visits in each city.
Results
Correlation coefficients between city-level GFT and ED visits for pneumonia and influenza from 19 different cities range from 0.67 to 0.93 with a median of 0.84. Coefficients are shown geographically in Figure 1.
Figure 1.
Geographic representation of 19 cities and their respective correlation coefficients for city-level GFT and influenza and pneumonia-related ED visits.
Conclusions
We demonstrate a strong correlation between city-level GFT and ED visits for pneumonia and influenza across numerous US cities. Establishing broad geographic generalizability of city-level GFT is key to understanding its capabilities and further integration into other surveillance or forecasting models.
Acknowledgments
This work was done in collaboration with the Agency for Healthcare Research and Quality (AHRQ). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of AHRQ.
References
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