The present medical consensus with regard to contagion is this:
Infected people are not contagious during the period before symptoms begin. This can be from 2 to 21 days after exposure. Apparently based primarily on how much virus the person was exposed to.
Once symptoms begin, the person is at first slightly contagious, with the degree of contagion increasing till he/she is wildly contagious during the final stages.
A person who survives may still be contagious for several weeks or perhaps months after acute symptoms end.
Any or all of the above may not be entirely accurate, but that is the medical theory at this point.
Good can come out of just about anything, no matter how terrible. This event will allow us to get some idea as to how effectively the spread of this disease can be controlled in a first-world nation as opposed to a third-world toilet. That’s good information to have. Next few weeks will tell.