Google Flu Trends in Canada: a comparison of digital disease surveillance data with physician consultations and respiratory virus surveillance data, 2010-2014.

The value of Google Flu Trends (GFT) remains unclear after it overestimated the proportion of physician visits related to influenza-like illness (ILI) in the United States in 2012-2013. However, GFT estimates (%GFT) have not been examined nationally in Canada nor compared with positivity for respiratory viruses other than influenza. For 2010-2014, we compared %GFT for Canada to Public Health Agency of Canada ILI consultation rates (%PHAC) and to positivity for influenza A and B, respiratory syncytial virus (RSV), human metapneumovirus (hMPV), and rhinoviruses. %GFT correlated well with %PHAC (ρ = 0·77-0·90) and influenza A positivity (ρ = 0·64-0·96) and overestimated the 2012-2013 %PHAC peak by 0·99 percentage points. %GFT peaks corresponded temporally with peaks in positivity for influenza A and rhinoviruses (all seasons) and RSV and hMPV when their peaks preceded influenza peaks. In Canada, %GFT represented traditional surveillance data and corresponded temporally with patterns in circulating respiratory viruses.