In the past, this particular team successfully tracked how influenza progressed on a national level, but there is a stark difference when it comes to regional and local differences in the manner on how influenza spreads. This has led the team to drop everything else and lay their eyes on the melting pot that is known as New York City, in order to figure out whether it is possible to discover local variations. Apparently, through the querying of billions of tweets and picking those that originate from New York City which so happened to make mention of the flu proved to be a masterstroke.
In fact, this research saw the tracked results to be rather close to traditionally gathered data on the 2012-2013 flu season. I guess this works only in countries where most folks own a smartphone and are well connected with social media.