Quantitative Epidemiological Understanding of Influenza Propagation Process in Tokyo and Environs

Here we show a quantitative, spatial interpretation of influenza propagation process in Tokyo and its environs in the season from November 1st, 2004 to October 31st, 2005. The time lags (day) of influenza propagation between distant sites are calculated by the cross-correlation functions of the daily variations in the amount of drug sale at community pharmacies. The influenza infection appears to have spread from the urban area of Tokyo to its suburbs in the season of 2004-05. From the time lags and distances of the pharmacy locations, the mean propagation speed is estimated to be 3.5 km/day.