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Seasonal flu often includes a fever above 38.5 C for two to four days.

Google Flu Trends, an internet search tool that tracks the spread of influenza as an early warning of outbreaks, expanded to Canada and 15 other countries on Thursday.

The company said it launched the tool in the U.S. last November after finding a close relationship between how many people searched for flu-related topics and how many people actually have flu symptoms.

"While some traditional flu surveillance systems may take days or weeks to collect and release data, Google search queries can be counted immediately," a posting on the official Google blog said.

"Google Flu Trends provides an additional surveillance tool that may help public health officials and the public make more informed decisions about preparing for the flu season."

Before the internet search company launched the service in the U.S., it compared its own data with official data from the U. S. Centers for Disease Control and Prevention and found similarities.

Parts of Europe included in expansion

The service gauges the level of infection in a particular location by tracking how many users in the same area search for terms like "flu symptoms" or "fever." 

Call a doctor?

On Wednesday, Microsoft Corp. unveiled a website that helps people worried about swine flu symptoms to decide whether they need medical attention.

The H1N1 Response Center is meant for people over 12.

It may conclude you likely have the H1N1 pandemic virus, but that rest and fluids should suffice.

However, if someone answers that they feel short of breath, or felt better but then a fever came back with a worse cough, the program would alert the user to call a doctor.

Thursday's expansion also includes much of Europe.

In the past year, Mexico, New Zealand and Australia were also added, and have also shown a good match between the company's estimates and official flu activity data, the blog post said.

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 email and the internet to track outbreaks of diseases such as avian flu. Its archive goes back to 1994.

In Canada, flu season usually runs November to April, and an estimated 10 to 25 per cent of Canadians may get the flu each year. Most recover completely, but an estimated 2,000 to 8,000 Canadians, mostly seniors, die every year from pneumonia related to flu, and many others may die from other serious complications, federal health officials say. 

With files from The Associated Press