Google Flu Trends

Google Flu Trends tracks flu-related search terms in selected countries around the world. (Notice that certain European countries, including the UK and Ireland, are not included.) I've added a screenshot of the world wide map, but an interactive feature allows you to look at a country, or its states or regions more closely.

The site tracks searches for flu-related topics because:

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 are added together. We compared our query counts with traditional flu surveillance systems and found that many 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 different countries and regions around the world. Our results have been published in the journal Nature.

(The links will take you to a pdf of the article.) Or you can click here and get a snapshot of the graph comparing Google Flu Trends estimate with US surveillance data. The difference? Google's maps are updated daily; in the US, the CDC updates its flu surveillance reports weekly. The CDC's flu site has a lot more detail, as you might expect.

Thanks to Jocelyn Bowie for the tip.