Google on Thursday expanded a flu-tracking tool to include 16 more countries, analyzing local patterns in search queries to determine the spread of the influenza.

Japan, Russia, and much of Europe are now included at Google Flu Trends. The California Internet powerhouse has also made information available online at google.org/flutrends/ available in 37 languages.

"Flu is a global threat, affecting millions worldwide each year, so we're pleased to make this tool available in more regions and languages," Google engineers Matt Mohebbi and Dan Vanderkam said in a blog post.

Google had already expanded Flu Trends to include Australia,Mexico, and New Zealand since launching the free influenza-tracking tool with US data in November of last year.

Flu Trends counts the number of flu-related queries on the GoogleInternet search engine and provides estimates on influenza outbreaks in respective regions.

Last season, flu spread estimates made using Google search terms closely mirrored data released by US health officials weeks later, according to Mohebbi and Vanderkam.

"By tracking the popularity of certain Google search queries, we are able to estimate the level of flu, in near real-time," the engineers said.

"While some traditional flu surveillance systems may take days or weeks to collect and release data, Google search queries can be counted immediately."

Google reports a strong correlation between Google searches for flu-related topics and how many people actually have symptoms of influenza.

"We filter out terms that may be popular because people hear about them in the news," Mohebbi and Vanderkam said.

For example, Flu Trends analysis filters out terms such as "swine flu" that people are likely to use when seeking news stories instead of because they are exhibiting symptoms of influenza.