Grey's Anatomy, Season 12

Meredith:
[opening voice-over] Infections have a nasty way of sneaking up on you. You're feeling pretty good, you think the infection is gone, and then, it reappears, out of nowhere. When your body's still weak, when you're barely recovered, BAM! You're infected all over again. And once the infection spreads, once it gets into your bloodstream, well, then you really have to watch it, cause that's the kind of infection that can kill you.