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:

Flu Information

Get more information on protecting yourself and keeping your family healthy during the flu season.


Vaccine Finder

Other Reporting/Analysis Sites

HealthMap Flu Near You

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  If you’re not a member of, 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.


Topics found in search queries which were found to be most correlated with CDC ILI data. The top 45 queries were used in our final model; the next 55 queries are presented for comparison purposes. The number of queries in each topic is indicated, as well as query volume-weighted counts, reflecting the relative frequency of queries in each topic.

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.