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Google Flu Trends Estimates Off

Google Flu Trends is not as accurate at estimating rates of laboratory-confirmed influenza as CDC national surveillance programs, according to a new study from the University of Washington. The findings will be reported at the American Thoracic Society 2010 International Conference in New Orleans.

"We knew from the Google Flu Trends validation study that it is highly correlated with surveillance for the non-specific syndrome of influenza-like illness," said Justin Ortiz, MD, clinical fellow at the University of Washington who led the study. "However, it has never been evaluated against a gold standard of actual laboratory tests positive for influenza virus infection. When we compared Google Flu Trends data to CDC's national surveillance for influenza laboratory tests positive, we found that Google Flu Trends was 25 percent less accurate at estimating rates of laboratory confirmed influenza virus infection."

Google Flu Trends uses the popularity of certain Google search queries in real time to estimate nationwide rates of influenza-like illness activity, a non-specific combination of symptoms including a fever with either a cough or a sore throat without any confirmatory laboratory testing. While some traditional flu surveillance systems may take days or weeks to collect and release data, Google search queries can be counted almost instantaneously.

The problem is that studies have shown that influenza-like illnesses are actually caused by the influenza virus in only 20 percent to 70 percent of cases during the influenza season.

"Many respiratory virus infections other than influenza can result in influenza-like illness. Furthermore, there is a wide and unpredictable proportion of influenza-like illness that is due to actual influenza virus," said Ortiz. "Because Google Flu Trends estimates of influenza-like illness may not necessarily correlate with actual influenza virus infections, we undertook this study to evaluate the validity of Google Flu Trends influenza surveillance by comparing it to a gold standard of CDC's national surveillance for influenza laboratory tests positive."

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