Well
There is so much here to comment on. And I am not very alert mentally.
But let's see.
First, I am glad they chose the sickest of the sick. As someone here said, many with diagnosis of CFS will not have a virus cause to their illness. Plus, it is possible that maybe this virus can also go into a latent or dormant stage. And the person may have CFS symptoms from the aftereffects, say an immune system gone awry, even though XMRV has been brought under control. One might expect that that person would not have the symptoms as severely as someone in an active XMRV infectious state. So, you could say that if WPI chose any patient with a CFS diagnosis, then the results would MORE skewed because they would have included ones with other illnesses, including psychiatric ones. And they would have included people who have the aftereffects, which would not help them in finding the virus, which was their goal.... see if the virus is there. This way, the only used ones with indisputable, true CFS and show signs of an active infection, if there is an infectious cause. They didn't include the cancer ones either. So the "not panning out" may be that others are using the broader definition in the cohort or those who had an infection, but not at the moment. Also, usually, they will separate them out in doing the study, usually in groups of 20-35. Then they will keep up with the results in the subgroups. I know CDC claimed it is including some WPI samples in their study. So they may see different results in the WPI samples than the ones of their own collection. But that should be documented.
Second, I would expect the CDC and other government agencies using the broader definition for their cohort will find a higher incidence of XMRV in their collection than healthy controls, but not as high as the cohort in the WPI study. Maybe they find 40% with active virus...?
Third, the study has already been verified by National Cancer Institute and Cleveland Clinic. They were co-authors, that means they banked their reputation on the information. So, there is definitely something there at an increase in the sickest of the sick of "CFS" patients. Cause not established, but definitely a retrovirus in greater incidence among them than healthy controls.
Now, remember this, as DeFrietas knows, viruses are not that easy to find in a microscope. It's not like you take a sample, put it under a microscope, and if the virus is there, the person has it and if they don't, the person doesn't. Ability to find a virus is determined by the level of infection. So narrowing to the sickest of the sick saves time and money. They are the ones who likely have more of the virus, thus it will be easier to find it, if it is there. Especially if a virus can go dormant, or the immune system has a response to it, you have to look for it. Think of how long it took them to find HIV in the blood of people with AIDS. Common sense would seem to indicate that you take the blood of an AIDS patient, put it under a microscope, and you should see, "Hey, there's a new virus in this person's blood that I haven't seen before." That's not the way it happened because viruses are very elusive. You can look at 100 cells and it not be in any of them, then you look in the next one and there it is. It's like looking for a needle in a haystack for some viruses. And as Defreitas said, some viruses will show in the blood for six days and then disappear. So this is not a simple, clean science. Even pap smears have probabilities of false negatives and false positives. Take that into account when the results for other researchers come in.
Tina