This winter if you start to get chills, high fever, headache, loss of appetite; severe muscle aches and pain, extreme fatigue and weakness then there is a good chance you've come down with the influenza, more commonly known as the "flu."

In its research, search giant Google has found that certain flu-related search terms appear to be excellent indicators of flu activity and last year created a site for Americans called Google Flu Trends. Today the company announced that Flu Trends has expanded to 16 additional countries including Canada.

The Google Flu trends website came about after a small team of Google software engineers began to explore if the company could go beyond simple trends and accurately model real-world phenomena using patterns in search queries.

In 2007, after meeting with the public health gurus on Google.org's Predict and Prevent team, the team decided to focus on outbreaks of infectious disease, which are responsible for millions of deaths around the world each year. One such disease: influenza, commonly known as "the flu," is responsible for up to 500,000 deaths worldwide each year, primarily among the elderly and immune compromised individuals.

In simple terms, more people queried Google on flu-related terms when they started getting the flu. Based on this discovery, Google launched Google Flu Trends, where you can find up-to-date influenza-related activity estimates for each of the 50 states in the U.S.

The reason Google's data was so fascinating for scientists is that traditional flu surveillance systems take 1-2 weeks to collect and release surveillance data, but Google search queries can be automatically counted very quickly. By making flu estimates available each day, Google believes its Flu Trends may provide an early-warning system for outbreaks of influenza.

So how good was Flu trends in its first year?

The good news is the company says analysis of last season shows that Flu Trends had a close 0.92 correlation with official U.S. flu data.

The bad news is, according to Google Flu Trends Canada , flu activity through October 6th is moderate already and trending well ahead of past years.

So get out your tissues and stock up on medicine

How Google Flu Trends works

The following is an explanation of how Google Flu Trends works, narrated by product manager, Dr. Roni Zeiger that discusses how Google built its model.