Yes, I do understand (I think) what you're trying to say.
As a non-doctor (nor nurse, nor any other medical professional), I have only a surface understanding of these concepts. It seems to me there must be a difference, medically, between someone who is a carrier and someone who has a virus and is on their way to becoming symptomatic but is not yet symptomatic.
MRSA carriers can still infect other people, right? So the same care must be taken with a MRSA carrier as with someone with an active MRSA infection.
And on the topic of being infectious, my understanding (again, as a non-medical professional) is that early on, before symptoms begin, there is such a low concentration of the virus in the person's system that infection is near-impossible. I'm not sure I accept that it's impossible, but I'll accept near-impossible. And as the quantity of virus increases, infection becomes more likely. (And especially at the end stages when the person is emitting huge concentrations of virus from every orifice.)
But to my knowledge, the docs/researchers don't know at exactly what stage of virus concentration contagion becomes "likely" vs. "not likely." And IMO, there wouldn't necessarily be a clear dividing line, but a continuum going from "near impossible" to "very likely." How certain are we -- how certain can we be -- that before symptoms manifest, the risk of contagion remains at the "near impossible" end of the spectrum?
That's exactly right. Virus builds up and person becomes more infectious. But I really don't think they can claim that before symptoms appear virus is impossible to catch. We know that Dr. Spencer's Ebola test came back positive on the first day he reported it.
So he already had enough virus in his blood to be detectable. Yet his fever wasn't even high enough.