What if the people who were already exposed are currently asymptomatic but contagious?

Same answer. Bob's decided to take something told in confidence and risk my reputation sharing it. He's not only a bad friend but clearly a risk so the best move is to burn him back and as hard as possible. He's getting dragged in and if he argues Im going to turn it into a larger issue for him. If we're coworkers I'm going straight to HR and asking what to do because a fellow employee infected me and then tried to put the blame on me. Anything but total calculated aggression will justify Bobs behaviors.

I guess it depends on whether you think someone has a right to a reputation independently of how they behave. Thanks for your answer, it was very enlightening.

To clarify, I'm aware there's a difference in perspective occurring. You're approaching it more from if it's beneficial to the larger group. But Bob is supposed to be my friend, if I can't trust him to keep something socially volatile like that a secret then he's failed me at an individual in a potentially harmful way. At an individual level it makes far more sense to bury Bob than say 'thanks for screwing me Bob'

Is your name Alice? I'm pretty sure I posed the question in the third person.