Google's Flu Trends tracks the frequency of search terms correlated with flu outbreaks throughout the world, country by country or even city by city. This year, data from the United States (along with Canada, Russia, and parts of Europe) shows 2013 to be an early and unusually intense flu season, the worst since Google began tracking flu data in 2006.

Google's data is so good as an early warning signal, the Center for Disease Control has made it an official partner. The CDC's traditional metrics of reported cases and hospitalizations also show this year's flu season to already be moderate to severe, depending on whether the growth curve peaks early and peters out or balloons outward. “In the past 10 years we have seen just two or three like it," said a CDC spokesman. The head of the Center's influenza division noted that "this particular strain circulating [the H3N2 virus] leads to more severe disease with more deaths and hospitalizations." Other complications include a concurrent burst in norovirus, laryngitis, respiratory syncytial virus, and whooping cough, all of which have symptoms similar to influenza.

In Boston, the mayor has already declared the flu outbreak a public health emergency, after confirming 700 flu cases (compared to just 70 all last year). Boston is offering free flu shots; it takes approximately two weeks for vaccinated patients to build an immunity, but if this year's flu turns into a genuine pandemic, this season still has months to run its course.