The key here is that, if we are to believe the newspaper article in the infirmary, Radical-6 is big enough to be a worldwide pandemic, yet none of the nine have heard of it before. A fair amount of time would need to pass for a new virus to be discovered and then get out of control, more time than the few days Sigma assumes it's been since his and the others' abduction. In fact, a way exists for the nine people in the compound to have been kept in stasis an indefinite amount of time - the cold sleep pods in the treatment room. I don't believe there's enough pods for everyone there, but there could easily be other pods elsewhere in the compound. Assuming that, I can suppose that all nine of them were kept in cold sleep for, say, 9 months (or years), 9 being the magic number after all, until it was time for the game to start. That gives Radical-6 enough time to spring up and spread in the outside world.
Moreover, considering the theme of "actions in the future changing the past", and Phi's statement that perhaps the world outside the compound is the box in which Schrodinger's cat is kept, I'm guessing that the reason for the nine's imprisonment is for them to perform some action that will change the past and prevent Radical-6 from causing widespread devastation. So, while they're in the compound, both the world in which Radical-6 is a problem and the world in which it isn't exist, and by the end they will make the right choices so that only the latter exists when they escape.
Not sure how the white liquid for Sigma plays into this yet; perhaps some cold sleep pods failed and the consciousnesses of those people were uploaded onto a robot.