Web searches might indicate spike in cases

By Miguel Helft
New York Times News Service / November 12, 2008
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SAN FRANCISCO - There is a new common symptom of the flu, in addition to the usual aches, coughs, fevers, and sore throats. Turns out a lot of ailing Americans enter phrases like "flu symptoms" into Google and other search engines before they call the doctor. That simple act, multiplied across millions of keyboards in homes around the country, has given rise to a new early-warning system for fast-spreading flu outbreaks called Google Flu Trends.

Tests of the new Web tool from, the company's philanthropic unit, suggest it may be able to detect regional outbreaks of the flu a week to 10 days before they are reported by the Centers for Disease Control and Prevention. In early February, for example, the CDC reported the flu had recently spiked in the mid-Atlantic states.

But Google says its search data show a spike in queries about flu symptoms two weeks before that report came out.

Its new service at analyzes those searches as they come in, creating graphs and maps of the country that, ideally, will show where the flu is spreading.

Some public health experts say the data could help accelerate the response of doctors, hospitals, and public health officials to a nasty flu season, reducing the spread of the disease and, potentially, saving lives.

"The earlier the warning, the earlier prevention and control measures can be put in place, and this could prevent cases of influenza," said Lyn Finelli, lead for surveillance at the influenza division of the CDC. Between 5 and 20 percent of the nation's population contracts the flu each year, she said, leading to an average of roughly 36,000 deaths.

For now the service covers only the United States, but Google is hoping to eventually use the same technique to help track diseases worldwide.

The premise behind Google Flu Trends - what appears to be a fruitful marriage of mob behavior and medicine - has been validated by an unrelated study indicating the data collected by Yahoo, Google's main rival in Internet search, can also help with early detection of the flu.

"In theory, we could use this stream of information to learn about other disease trends as well," said Philip M. Polgreen, assistant professor of medicine and epidemiology at the University of Iowa and a co-author of the study based on Yahoo's data.

Other people have tried to use information collected from Internet users for public health purposes. A website called invites people to report about what ails them and superimposes the results on a map. But the site has received relatively little traffic.

HealthMap, a project affiliated with Children's Hospital Boston and Harvard Medical School, scours the Web for news articles, blog posts, and electronic newsletters to create a map that tracks emerging infectious diseases worldwide. It is backed by, which counts the detection and prevention of diseases as one of its main philanthropic objectives.

But Google Flu Trends appears to be the first public project that uses the powerful database of a search engine to track the emergence of a disease.

"This seems like a really clever way of using data that is created unintentionally by the users of Google to see patterns in the world that would otherwise be invisible," said Thomas Malone, a professor at the MIT Sloan School of Management. "I think we are just scratching the surface of what's possible with collective intelligence."

Still, some public health officials note many health departments already use other approaches, like gathering data from visits to emergency rooms, to keep daily tabs on disease trends in their communities.

"We don't have any evidence that this is more timely than our emergency room data," said Farzad Mostashari, assistant commissioner of the New York City Department of Health and Mental Hygiene. If Google provided health officials with details of the system's workings so it could be validated scientifically, the data could serve as an additional way to detect influenza that might prove valuable, said Mostashari, who is also chairman of the International Society for Disease Surveillance.

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