When the first U.S. patients fell victim to the H1N1 flu, they may not have first called the doctor. Instead, they probably sat down in front of their computers and Googled flu symptoms. That's exactly what the folks at Google have been counting on. Since 2008 the search-engine giant has been nurturing a service called Google Flu Trends, which aims to identify outbreaks by tracking searches for flu-related terms and providing health officials with warnings. The World Health Organization uses a similar surveillance strategy, mining media reports to suss out mentions of unusual illness. And the Centers for Disease Control and Prevention has a network of physicians who routinely test a sample of patients to see which bugs might be circulating in their communities.