Correlation of “Google Flu Trends” with Sentinel Surveillance Data for Influenza in 2009 in Japan

Google Flu Trends (http://www.google.org/flutrends/) (GFT) aggregates Google search data to estimate flu activity in 28 countries. This study explored the correlation of GFT with Japanese national sentinel surveillance data in 2009. We obtained GFT and national sentinel surveillance data for influenza in all 47 Japanese prefectures from 29 June– 31 Dec 2009. Pearson correlation coefficients were calculated between GFT and sentinel surveillance data in each prefecture. Multiple regression analysis was also used to determine associations between them. Correlation coefficients were greater than 0.9 between GFT and the sentinel surveillance data in Tokyo, Kanagawa, Aichi, Osaka, and Hyogo, which have relatively large populations. Peaks for GFT were 2 weeks earlier than sentinel surveillance in these prefectures. Multiple regressions showed that only Tokyo (r = 0.97; P < 0.01) was significantly associated with GFT. People’s interest in influenza affects GFT data, which could reflect influenza spread in mega-cities such as Tokyo. Further development of technology to identify prefecture-wide epidemic patterns could offer more accurate information on influenza spread in Japan.