Mullins attributes the CDC's early use of social media to its highly trusted brand among the public, making it easier to partner with other organizations on the Web.

The CDC's use of social media has so far included virtual worlds, podcasts, RSS feeds, Facebook, MySpace, widgits, chats and eCards. Electronic greeting cards, or eCards, have been adapted by CDC for sending health messages rather than birthday greetings and typical eCard messages. A friendly reminder from a trusted source to get cancer screenings, for example, is much more effective than a public service announcement, and people can find eCards online alongside Web sites that address  particular health topics.

"It doesn't make sense for us to have a site for this when there are sites already out there that have large constituencies around various healthcare topics," Mullins said.

This Valentine's Day, the CDC reported, 6,000 of its e-Cards were sent with health messages.

Over the past couple years, the CDC has partnered successfully with a popular virtual world called Whyville for youths aged 12-14 to present messages on seasonal flu. In 2007, some 41,000 visitors to the site had their avatars vaccinated against the fictitious Why flu in the virtual world, including a surprising 1,800 seniors who play the game online with their grandchildren. Through the use of Whyville, CDC officials had an opportunity to teach both young teens and seniors about the importance of flu vaccinations and piqued interest in other CDC prevention topics, Mullins said.