They were expecting secondary cases, al
@Professor Toffee may know more than me, but as far as testing early... I don't know if a negative test prior to symptom development is definitive. Even one test is not cost effective if it does not definitively rule out infection. These aren't cheap tests.
You often need to have a high enough viral load for a test to detect the presence of the virus or antigen. I would wonder if the viral load that starts to produce symptoms correlates to being able to detect the virus in a test. Semi-educated speculation here...infectious disease is not my speciality.
As far as the medications, like ZMapp... we honestly don't know if they work. Would the people that took it have survived anyway? And we have no clue what the adverse effects of the drug might be. It was a major medical ethics issue to give the drugs to people with active disease, so imagine if patients are not sick. First do no harm and all that....
We have no idea if it really works in active disease so we are even more clueless about using these drugs to prevent a symptomatic illness.
Also with an extremely limited supply of the meds, it's going to go to the sick first. Remember these drugs were in the testing phase. There were only a few doses on hand although they are ramping up production now.