Alcohol won't kill a virus. Sterilize with heat or bleach.
Viruses are spread by exchange of bodily fluids. That means if you cut a dead leaf off an infected plant, or break a root or clip an old flower stock or... And then move on to another plant without sterilizing your hands and tools and work surface, you will pass it on to a new unsuspecting plant.
The reason for separating the maybe infected plant from the others is viruses are also spread by sucking insects (mealy bugs, scale...).
You can keep your orchid, just be extremely careful. When I suspected one of my orchids had a virus, I found someone at my orchid society meeting willing to sell me one test. It very easy to administer.
