Flu Trends

We've found that certain search terms are good indicators of flu activity. Google Flu Trends uses aggregated Google search data to estimate current flu activity around the world in near real-time.

Each week, millions of users around the world search for online health information. As you might expect, there are more flu-related searches during flu season, more allergy-related searches during allergy season, and more sunburn-related searches during the summer. You can explore all of these phenomena using Google Insights for Search. But can search query trends provide the basis for an accurate, reliable model of real-world phenomena?

Australia, New Zealand and the United States

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 states and countries around the world. Our results have been published in the journal Nature.

These graphs show historical query-based flu estimates for different countries and regions compared against government influenza surveillance data. As you can see, estimates based on Google search queries about flu are very closely matched to traditional flu activity indicators. Of course, past performance is no guarantee of future results. Our system is still new, but we're hoping to see similar correlations in the coming years.

Governments and health agencies use a variety of methods to track influenza around the world. One method relies on doctors to keep track of the percentage of their patients who have an influenza-like illness, also known as an "ILI percentage". Many governments and health agencies collect and aggregate this data each week, providing a good indicator of overall flu activity in their area.

So why bother with estimates from aggregated search queries? Traditional flu surveillance is very important, but most health agencies focus on a single country or region. Many traditional surveillance systems don't publish their results online each day. Unlike these systems, Google Flu Trends is currently available for several countries around the world, and will grow to include more countries in the coming years. By making our flu estimates available each day, Google Flu Trends may provide a global influenza surveillance system with early-warning for influenza outbreaks. Flu Trends is designed to be a complement to existing surveillance systems, not a replacement.

For epidemiologists, this is an exciting development, because early detection of a disease outbreak can reduce the number of people affected. If a new strain of influenza virus emerges under certain conditions, a pandemic could ensue with the potential to cause millions of deaths (as happened, for example, in 1918). Our up-to-date influenza estimates may enable public health officials and health professionals to better respond to seasonal epidemics and pandemics.

To learn more about the research behind Google Flu Trends, please read Detecting influenza epidemics using search engine query data, published by Nature (PDF available here). To further explore the data behind Google Flu Trends you can download CSV spreadsheets containing Google Flu Trends estimates going back several years.

Mexico (Experimental)

In response to inquiries from public health officials regarding the H1N1, or swine flu, outbreak that started in April 2009, we built experimental models for Mexico. You'll see our unverified estimates on the Experimental Flu Trends for Mexico page. We hope this may shed additional light on possible flu activity in Mexico.

Unlike Google Flu Trends for Australia, New Zealand and the United States, Experimental Flu Trends for Mexico was not built using historical data on flu symptoms. This means the models have not been checked against actual historic flu data from Mexico, and thus, the estimates you see for Mexico are unverified. The models for Mexico are based on aggregated search queries likely to be associated with influenza-like illness (ILI).

Protecting User Privacy

At Google, we are keenly aware of the trust our users place in us, and of our responsibility to protect their privacy. Google Flu Trends can never be used to identify individual users because we rely on anonymized, aggregated counts of how often certain search queries occur each week. We rely on millions of search queries issued to Google over time, and the patterns we observe in the data are only meaningful across large populations of Google search users. You can learn more about how this data is used and how Google protects users' privacy at our Privacy Center.