The Internet giant's philanthropic arm has been doing the same for the United States at its Google Flu Trends website since late 2008 but global spread of an influenza strain traced to Mexico prompted a longer reach.

"We launched Google Flu Trends after finding a close relationship between how many people search for flu-related topics and how many people actually have flu symptoms," Google software engineers Jeremy Ginsberg and Matt Mohebbi said in a blog post at the California firm's website.

"Google Flu Trends may be able to detect influenza outbreaks earlier than other systems because it estimates flu activity in near real time."

Inquiries from public health officials led Google to try using levels of searches on flu-related topics to make reliable, real-time estimates of actual cases of influenza in Mexican states, Ginsberg and Mohebbi wrote.

"Experimental Flu Trends for Mexico is, as you might have guessed, very experimental," the software engineers cautioned.

"But the system has detected increases in flu-related searches in Mexico City and a few other Mexican states in recent days, beginning early in the week of April 19-25."

While Google has been able to check Flu Trends estimates against statistics gathered by the US Centers for Disease Control and Prevention, a similar verification option does not exist in Mexico.

Google's new Mexico Flu Trends map indicated "moderate" levels of flu activity in about a half dozen spots including Oaxaca, Veracruz, Tamaulipas and Jalisco.

Google Flu Trends estimates of flu activity in the United States continued on Wednesday to be rated "low" but the engineers said they are vigilantly "keeping an eye on the data to look for any spike in activity."

President Barack Obama warned Wednesday that "utmost precautions" were needed to contain the outbreak as the first fatality was reported in the United States, a Mexican toddler who died in a Houston hospital.

Facebook, meanwhile, has begun tracking flu-talk involving US members of the world's most popular social-networking website.

A Facebook page titled "Mapping the Swine Flu Discussion" features a color-coded US map showing what percentages of users in states have referred to the recent influenza scare in messages posted on profile "walls."

Facebook's map showed the topic was hottest in Texas, where about 0.8 percent of users had posted influenza-related comments to friends.

"Looks like Texas is pretty scared of getting it from Mexico," a Facebook user going by the screen name Andrew Edgerton commented in a forum linked to the service's flu map.

Comments ranged from terror that the flu will be a deadly scourge of apocalyptic proportions to belief that news hype and online exchanges are fueling hysteria.

"Swine flu may be a threat, but the media is just blowing it up, and causing unnecessary anxiety," wrote Facebook user Timothy Españo Alconga.

Flu-related comments flooded Twitter at rates of thousands per hour, with references to the topic claiming five spots on the micro-blogging service's Top Ten list of trends.

"I'm worried ... this swine flu pandemic is some serious (stuff)," a Twitter user wrote under the onscreen name Jazzamatazz. "I recall reading something in the bible (Revelations) about this and it's scary."

A Twitter user by the name auntdodi countered with "Nothing but disdain for swine-flu. Fear-mongering media got me worked up about bird flu. I will not fall for that again."

The CDC itself has been using Twitter to fire off influenza updates.

The World Health Organization on Wednesday raised its flu alert to phase five out of six signaling that a pandemic was "imminent" following the swine flu outbreak.

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