Google revamps Flu Trends after it overestimated illness

Google says it is revamping its online flu tracking system after it vastly overestimated the number of U.S. flu cases in recent seasons.

Google Flu Trends launched in the U.S. in 2008, aiming to document and predict the spread of the flu based on how many people were searching for flu-related terms online. "We do hope it can help alert health professionals to outbreaks early, and in areas without traditional monitoring, and give us all better odds against the flu," the company said in a blog post.

At first, Google said its results seemed to be remarkably accurate when compared with official data released by the Centers for Disease Control and Prevention.

However, in the 2012-2013 flu season, Google's numbers were way off. Research published by Google and analysis in the journal Nature found the Flu Trends algorithm overestimated the number of cases during peak flu season by more than 100 percent - predicting twice as many cases as actually happened.

What went wrong? Apparently, spikes in search traffic by people worried about the flu were skewing the results, even when most of them didn't actually have it.

"We hypothesized that concerned people were reacting to heightened media coverage," Google researchers wrote. The algorithm was designed to take into account short-term spikes in search traffic based on media coverage, but Google wasn't expecting the effect to last all season.

This prompted them to revise the algorithm last year "to insulate the model from this type of media influence." The 2013-2014 Flu Trends data proved somewhat better, the company said without releasing specific figures, but it still saw room for improvement.

So for the upcoming flu season, Google now says it will incorporate CDC data on confirmed flu cases into its calculations as the season progresses, to try to get more valid results and counteract the effect of too many "worried well" people doing flu searches.

Flu season can begin as early as October and normally peaks between December and February. The CDC recommends almost everyone over the age of 6 months get the flu vaccine -- available as either a shot or nasal spray -- to protect against getting sick. Children under the age of 5, pregnant women, and seniors over the age of 65 are most at risk of developing serious complications from the flu, the CDC says.

Google Flu Trends tracks influenza in the U.S. and 28 other countries across the globe. The company has also launched Dengue Trends to track cases of dengue fever, an illness spread by mosquitoes in tropical climates that the World Health Organization estimates infects 50 to 100 million people worldwide each year.