The big fluenza measurement

This week started in different European countries a specific experiment, where the number of people who're having the flue are measured. This way, the creators of the big fluenza measurement hope to chart the progress of the flue in these European countries.

I'm having questions though with the scientific validity of such a test : picturing the spreading of the flue in this way can only be valid if there's not much mobility between different parts of the regions, and in Belgium with its large number of commuting people, it is clearly not the case.