"Question: All our Knockout roses died this summer from that virus you wrote about. Can we plant new ones this fall or is the soil contaminated with this disease?
Answer: There are still a lot of unanswered questions about this virus. However, the consensus from plant pathologists is that the virus does not live in the soil. Although the virus has been around for decades, little is known about the transmission of this virus. If you plant new Knockouts in the same flowerbeds where the previous ones were, be sure all roots of the older plants are removed. It is recommended that roses be planted further apart to avoid touching one another as they age. I would suggest a minimum of 6 feet apart. It has been observed by other horticulture professionals that this virus less affects the single red and pink Knockouts than the double reds. Please do not read into this statement that they will never get it. All roses are subject to this virus including the wild ones. Just be sure the new plants have no sign of this disease when purchased. Hopefully someone can spot this disease before you buy them."

The above quote from:
http://www.thetimesnews.com/news/local-columnists/rett-davis/frequent-fescue-fertilization-rose-viruses-1.238930

Here is a link that might be useful: link for above from Burlington, North Carolina