An internet search tool could be helpful in tracking the spread of influenza cases in the U.S. and act as an early warning of an outbreak, according to an expert at the U.S. Centers for Disease Control.

Google Flu Trends will analyze patterns based on how often people search for flu-related terms and plot their locations in near real time, the company said.

'The data are really, really timely. They were able to tell us on a day-to-day basis the relative direction of flu activity for a given area.'— Dr. Lyn Finelli

"One thing we found last year when we validated this model is it tended to predict surveillance data," said Dr. Lyn Finelli, chief of influenza surveillance at the U.S. Centers for Disease Control.

"The data are really, really timely. They were able to tell us on a day-to-day basis the relative direction of flu activity for a given area. They were about a week ahead of us. They could be used … as an early warning signal for flu activity."

The early warning could help hospitals prepare for a surge in patients during flu season, as well as track flu activity in case of a pandemic.

Results from the free, web-based method will be shared with the CDC, but individual user data will be kept confidential, Google software engineers Jeremy Ginsberg and Matt Mohebbi said in the company's blog.

The CDC currently relies on reports from doctors who see people with flu-like symptoms and lab test results, so those who never see a health professional are left out of influenza surveillance reports.

"Certainly the thinking is innovative," said Dr. Keiji Fukada, co-ordinator of the global influenza program at the World Health Organization in Geneva. "But I think that we know what the search engine is going to pick up is interest in influenza and that may not necessarily mirror disease at the time."

Online outbreak tracking

Google Flu Trends is currently available in the U.S. only, although the company said it hopes to include other countries and diseases.

Google's mapping tool, Google Earth, is already used to track outbreaks of avian flu.

A Canadian-developed technology called the Global Public Health Intelligence Network launched in 2004 to act as an early warning system to prevent outbreaks and possible bioterrorist attacks worldwide, based on information from media reports and websites in seven languages.

The non-profit Program for Monitoring Emerging Diseases, or ProMED, an online global reporting system run by the International Society for Infectious Diseases, has also used e-mail and the internet to track outbreaks of diseases such as avian flu. Its archive of incidents goes back to 1994.

Influenza is a highly contagious respiratory disease. Common flu symptoms include fever, muscle aches and cough. While flu and cold symptoms can be similar, influenza is much more serious because it drastically reduces the body's ability to fight off other infections.

In Canada, flu season usually runs from November to April and an estimated 10 to 25 per cent of Canadians may get the flu each year. Although most recover completely, an estimated 4,000 to 8,000 Canadians, mostly seniors, die every year from pneumonia related to flu, and many others may die from other serious complications, according to Health Canada.

With files from Reuters, Australian Broadcasting Corp.