Alex, I don't know about the CDC test, but the WPI's and FDA's test did use an annealing temperature (and probably other things as well) that allowed them to find viruses that are not identical or almost identical to XMRV VP62. Had the FDA used a method that focused on specificity instead of sensitivity, they would probably find nothing, and then it's possible that you would have heared Dr. Lo and Dr. Alter supporting the contamination theory. See, it's those very small things that makes this huge difference. The WPI sequenced every PCR PRODUCT that they had (meaning - everytime that the PCR came up positive - they sequenced the PCR product, which is just a part, pretty small part, of the virus), and also sequenced full XMRV genomes from 2 of the positive patients, and one partial genome (which I guess was much bigger than a PCR product) of a third patient. In the full genomes, they found that they are different from VP62 in just 6 nucleotides - out of 8,185 nucleotides - meaning that it is more than 99.9% identica to VP62, although not 100% identical. However, these are only two full genomes out of 107 people in which they found evidence for XMRV/MRV infection (not including the britain study and others). So, at first it seemed that they found things that a test that would be very specific to VP62 would find - but now it doesn't seem that way, and although it was probably not expected, it still is reasonable, as they had then only 2 full length sequences. However, I have to explain - as far as I understand it, by sequencing their PCR products they are making sure that the things that they find are XMRV or at least MRVs, and not, for example, EBV... So there is absolutely no need to be worried about that - that is what is done when you do nested PCR.