I think it might be a question of what procedures and tests did he use. First of all, if he used only one PCR test, than if you see the numbers of the WPI's study when they used only PCR - you get 7% of XMRV positives, when the real numbers are about 80%-90% (this is about 57 patients - not all of the patients). Second of all - it might be a question of collection and proccesing. Dr. Mikovits have talked about the blood working group discovering that it is a crucial part of the testing. I guess that it might cause a scientist to not be able to find XMRV even if the person who has beewn checked do have XMRV in the peripheral blood. Dr. Levy might be a well respected virologist/retrovirologist, but XMRV is a new virus and the people who know the most about it right now are people such as Dr. Mikovits, the Ruscettis, Dr. Silveman, Dr. Klein, Dr. Singh etc., and probably not yet Dr. Levy.