If a plant is showing signs and then tests positive for virus, I would assume that it is virused. I would dispose of the plant, but what you want to do is up to you. As far as the other plants, they may or may not be infected. In general, testing is the best way to confirm virus. Any plants that were in contact with the virused plant should probably tested and/or grown separately from other plants. Virus is spread by direct contact-sap to sap or through contaminated tools, but is not spread by air. I would definitely keep any new plants away from possibly infected plants. It's a good idea to quarantine new plants in general before growing with the rest of your plants.
I would also tell the company. There are things that they can do, but may or may not choose to.