Using the same keyword tracking technology found on Google Trends, it keeps an eye on people searching for queries involving the word "flu" and tracks them both by date and location.
What makes the technology so fascinating is that its data set goes back to 2003, and has been cross-referenced with the last several years of survey data from the Centers for Disease Control and Prevention (CDC). Google says that because its own system is based on a constant flow of searches as opposed to surveying techniques it's able to provide results one to two weeks faster than the CDC.
The same trending technique could be used in tandem with other organizations to track contagious viruses or threats besides the common cold, including AIDS, bird flu, and Africanized honey bees.
One limitation of the current system is that it does not track worldwide flu traffic. There is, however, quite a bit to discover from data from years prior--especially when you get several years that stack up on top of each other with similar rises and falls during certain parts of the year. According to Google's chart, we're about three weeks from hitting the heavy season, which goes until early January.
By Josh Lowensohn