The Google initiative is being well-received by public officials, the Google engineers said.

"We shared our preliminary results with the epidemiology and prevention branch of the influenza division at CDC throughout the 2007-2008 flu season, and together we saw that our search-based flu estimates had a consistently strong correlation with real CDC surveillance data," they blogged. "Our system is still very experimental, so anything is possible, but we're hoping to see similar correlations in the coming year."

Influenza, they noted, is responsible for up to 500,000 deaths each year.

Ginsberg and Mohebbi said they couldn't have created such good models without aggregating hundreds of billions of individual searches going back to 2003.

"Of course, we're keenly aware of the trust that users place in us and of our responsibility to protect their privacy. Flu Trends can never be used to identify individual users because we rely on anonymized aggregated counts of how often certain search queries occur each week. The patterns we observe in the data are only meaningful across large populations of Google search users."

As a healthcare professional, tell us what you think of Google's flu tracking. Send your comments to Bernie Monegain at bernie.monegain@medtechpublishing.com.