Google has a Flu Trends project where you can see influenza trends across the world estimated by search queries.
Here’s an example from my state, Pennsylvania:
Get more information on protecting yourself and keeping your family healthy during the flu season.
Other Reporting/Analysis Sites
How Does Google Do It?
I found myself wondering what search terms they are using to evaluate flu trends. It was actually quite interesting to read the article published by Nature.com. If you’re not a member of Nature.com, you can still download the article from Google in PDF format.
Reading over the article, I looked at the following table to see how they weighted queries from search data.
Google, in the article, states the following:
Because the relative frequency of certain queries is highly correlated with the percentage of physician visits in which a patient presents with influenza-like symptoms, we can accurately estimate the current level of weekly influenza activity in each region of the United States, with a reporting lag of about one day.