Since last year, 36 people have died from a virulent strain of bird flu, transmitted largely from infected poultry stocks. Now there's evidence that the virus can jump from human to human, and health officials worry that it's only a matter of time before the flu evolves its transmission mechanism and starts a worldwide pandemic. Guest host Bruce Gellerman speaks with Dr. Jeremy Farrar, who's treating patients with symptoms of the avian flu in Vietnam's Ho Chi Minh City.