Google Flu Trends counts the number of flu-related queries on the Google search engine and provides estimates on influenza outbreaks in each of the 50 states in the US.

'We found that there's a very close relationship between the frequency of these search queries and the number of people who are experiencing flu-like symptoms each week,' the Internet giant said on Tuesday in a posting on its official blog.

Apparently, many Americans who are down with flu enter phrases like 'flu symptoms' into Google and other search engines before they call their doctors.

'If we tally each day's flu-related search queries, we can estimate how many people have a flu-like illness.'

Google said it had shared its results with the Atlanta-based US Centres for Disease Control and Prevention (CDC), which does its own flu tracking.

'It turns out that traditional flu surveillance systems take one to two weeks to collect and release surveillance data, but Google search queries can be automatically counted very quickly,' Google said.

'Together with the CDC, we saw that our search-based flu estimates had a consistently strong correlation with real CDC surveillance data,' it added.

In early February, for example, the CDC reported that the flu cases had spiked in the mid-Atlantic states. And Google said its search data show a spike in queries about flu symptoms two weeks before that report was released.

The CDC reports are slower because they rely on data collected and compiled from thousands of health-care providers, labs and other sources.

Google cautioned that Google Flu Trends, which can be seen online at google.org/flutrends, is 'still very experimental,' but said it could possibly be a useful tool in preventing the spread of other diseases.

'By making our flu estimates available each day, Google Flu Trends may provide an early-warning system for outbreaks of influenza,' the Mountain View, California-based company said.

'Our up-to-date influenza estimates may enable public-health officials and health professionals to better respond to seasonal epidemics and - though we hope never to find out - pandemics,' it added.

'The earlier the warning, the earlier prevention and control measures can be put in place, and this could prevent cases of influenza,' said Dr Lyn Finelli, lead for surveillance at the influenza division of the CDC.

Between 5 and 20 per cent of the nation's population contracts the flu each year, she said, leading to roughly 36,000 deaths on average. Around the world, influenza is responsible for some 500,000 deaths each year.

Google hopes to eventually use the same technique to help track influenza and other diseases worldwide.

'From a technological perspective, it is the beginning,' said Mr Eric Schmidt, Google's chief executive.

'This seems like a really clever way of using data that is created unintentionally by the users of Google to see patterns in the world that would otherwise be invisible,' said Professor Thomas Malone of the Sloan School of Management at the Massachusetts Institute of Technology.

'I think we are just scratching the surface of what's possible with collective intelligence.'

AGENCE FRANCE-PRESSE, NEW YORK TIMES