Googling the Flu

Official reports of swine flu cases always lag behind actual cases. It takes time for people to get to a doctor, get diagnosed, and have the results reported to public health surveillance networks. And that assumes people get checked out: illegal aliens and other uninsured people in the U.S. might try to treat themselves and stay under the radar. But you don’t need health insurance or a doctor’s appointment to use Google. Led by research showing that the popularity of certain search terms correlates with a rise in the incidence of flu, the company just published flu estimates for 16 states in Mexico and the country as a whole, as well as U.S. data, in an effort “to help track the spread of the swine flu outbreak,” Google said in a statement.

The effort began last week, when epidemiologists at the U.S. Centers for Disease Control and Prevention asked the researchers at Google Flu Trends if they could track the incidence of swine flu in Mexico. Google Flu Trends, which was launched last November, analyzes the popularity of various search terms to detect a sudden increase in flu cases: historical data have shown that when lots of people start Googling terms such as “flu,” “aches,” “fever” and “buy thermometer,” it correlates with a rise in flu cases. (The researchers described their methodology in a February paper in Nature.) By comparing historical search data with historical data on flu cases, the Google team has been able to filter out search terms—such as plain old “swine flu”—that indicate curiosity rather than an actual case of the flu.

It’s not clear if the Mexican search data are reliable, however. Unlike for the U.S., Google does not have data correlating actual flu incidence in Mexico with the popularity of particular search terms among people in Mexico. The lack of such historical data means the Google researchers “cannot be fully confident that the data is correct,” they say. But “we are cautiously optimistic that the graphs reflect actual flu activity. . . . While we would prefer to validate this data and improve its accuracy, we decided to release an early version today so that it might help public health officials and concerned individuals get an up-to-date picture of the ongoing swine flu outbreak.” Google Flu Trends will update the Mexican data every day.

Interestingly, Google Flu Trends shows low flu activity in the U.S. While it’s too soon to breathe a sigh of relief, that just might be an indication that public health authorities are not missing a huge number of swine flu cases, which as of 11 a.m. today numbered 91 in 10 states with one fatality. Google Flu trends promises, however, that it will “be keeping an eye on the data to look for any spike in [U.S.] activity.”