Comparison of epidemic intensity during the 2009 A/H1N1 influenza pandemic and the 2012/2013 seasonal A/H3N2 epidemic as measured by Google Flu Trends (GFT) and public health influenza-like illness (ILI) surveillance at the national (United States), regional (Mid-Atlantic) and local (New York City)

Epidemic intensity was measured by Serfling regression of weekly percent-ILI for public health surveillance data and GFT estimates for peak week and seasonal epidemic excess, with corresponding upper and lower 95% limit, calculated as the predicted non-epidemic baseline +1.96 standard deviations.