Generally I wouldnt think so, except the way you said the rash started and then spread. That sounds just like rubella. Can you actually FEEL the rash when you run your fingers over it? If you stretch the skin, does it kinda disappear? Does it seem to move around a little, like when it went to his arms, did it kinda disapate from his back? I had mistaken Roseola for measles in DS1 last year, and these are all the steps the PED had me go through over the phone before bringing him in, (which we didnt end up bringing him in cuz he "passed"). Is the fever gone completely, or is it up and down?