Google.org has released Flu Trends, an online reporting tool for flu-related search activity. It’s long been theorized that Google’s search data would be useful to predict epidemics. This is the first time they’ve released a tool like this to the public. As they say on the main page:
We have found a close relationship between how many people search for flu-related topics and how many people actually have flu symptoms. Of course, not every person who searches for “flu” is actually sick, but a pattern emerges when all the flu-related search queries from each state and region are added together. We compared our query counts with data from a surveillance system managed by the U.S. Centers for Disease Control and Prevention (CDC) and discovered that some search queries tend to be popular exactly when flu season is happening. By counting how often we see these search queries, we can estimate how much flu is circulating in various regions of the United States.
[Update, 14 May 2009: Google is refining their Flu Trends data by asking people questions about their flu searches.]