Well...how it works huh? Computer users, especially those who rely almost everything on the technology might use Google to search for everything, including remedies or methods to solve influenza etc. So, Google actually use this to track how many people in that state are requesting for help and so, it detects flu outbreaks. Amazingly, this way is actually 2 weeks faster than the data collected by CDC(Centres for Disease Control and Prevention). If you still wondering how they can locate your position or which state you are in, that is through your IP address. Each IP address is unique and tells which district you are in now. So, when your state is indicated as high flu outbreaks, you can consider of buying some medicines or get yourself a jab before you get it. Doctors also use this tool to pay more attention to their patients if they see that the rate is quite high around that area. This could definitely reduce the disease widespread.
Look for the video from CNN here.