Bill Gates spoke with broad optimism about the potential for technology to address some of the globe's biggest challenges, but struck an ominous tone Friday in discussing the threat posed by the coronavirus as the outbreak outpaces the best efforts of doctors and health workers.

The impact could be "very, very dramatic," the billionaire philanthropist said, addressing a standing-room-only audience during his keynote address at the American Association for the Advancement of Science annual meeting in Seattle. He called it a "potentially very bad situation."