Google's search data may have been able to provide an early warning of the swine flu outbreak — if the company had been looking in the right place.

Last week, at the request of the Centers for Disease Control, Google took a retroactive look at its search data from Mexico. And there the team found a pre-media bump in telltale flu-related search terms (you know, "influenza + phlegm + coughing") that was inconsistent with standard, seasonal flu trends.

"We did see a small increase in many parts of Mexico before major news coverage began last week," said Jeremy Ginsberg, lead engineer for Google.org's Flu Trends.

But the Google Flu Trends team, which aggregates and analyzes search queries to estimate how many people are sick, wasn't watching Mexican flu data until after the outbreak had already begun. That highlights the problem with tech-heavy disease-detection systems: Often, we don't know what internet data to look at until after a problem starts.

The early signals of disease are hidden in plain sight, and it takes humans recognizing that something is happening before the computers can be asked to find it. And even if Flu Trends had picked up a noticeable bump in flu searches in Mexico early, a lot of additional analysis would have been required to understand the potential severity of the pandemic.

But it's encouraging to think that if the Flu Trends system were built out across the globe, it might sound an early alarm about the next unusual flu outbreak. You can check out the data yourself at the site, Experimental Flu Trends for Mexico, launched today.

Ginsberg cautioned, though, that the correlation between the Mexican flu-search terms and actual epidemiological data hadn't been verified. For the U.S. version of Flu Trends, the Google engineers have been able to check their equations and graphs against actual reported cases of flu. It turns out their system tracks the CDC data quite nicely.

The U.S. version of Flu Trends also appears to be handling the latest swine flu epidemic well. The system hasn't reported large upticks in states like New York, where the number of cases remains still quite small relative to standard seasonal flu infections. That means that people simply searching for swine flu or #swineflu aren't generating false-positive spikes in Flu Trends.

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Image: Screenshot, Google.

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