"We were able to take serum frozen in 1984—at the time I asked for the CDC's help with this disorder—thaw it, and infect cells [with XMRV] and that is very dramatic to me. It's somewhat frightening," the doctor continued, "that you can take blood that's been frozen for twenty-five years and obtain active infective virion."
An aside, a parenthtical phrase setting the time frame; Peterson didn't even have to mention it, but he did. Jerry Crum, and by inference the other patients in that outbreak, was fulminantly infected with XMRV in 1984, the year Peterson had asked CDC for help. Had CDC actually helped when he asked in 1984, maybe it would have been the CDC growing XMRV out of that frozen blood, not the Nevadans, and maybe it would have happened a decade or two ago.