This study seems to add some support to the idea that XMRV may be another secondary infection of CFS similar to HHV6 and EBV rather than the primary cause of CFS. If XMRV is the primary cause of CFS the way that HIV is the primary cause of AIDs then every person that has CFS must be infected with XMRV/MLV. This would mean that the XMRV negative patients would only be negative due to false negatives in the XMRV/MLV diagnostic test. However, false negatives in the diagnostic test should have no effect on treatment outcomes, since everyone with CFS would be infected with XMRV/MLV, with some just not showing up on the diagnostic test. The fact the XMRV positive patients responded much stronger to treatment with Ampligen than XMRV negative patients means that something else may be causing CFS which damages the immune system, which then allows XMRV to infect some CFS patients as a secondary infection. In this case, assuming Ampligen is an effective treatment for XMRV infection, the XMRV infected subset would see greater improvement in symptoms compared with the XMRV negative group, just like treating for HHV6 would show a greater improvement in symptoms for HHV6 positive patients compared to HHV6 negative patients.
As I mentioned before, its CFS that we want to treat, cure, and prevent. If XMRV/MLV is the cause, then great, we are all the closer. If not, then at least it has brought CFS a great deal of attention from the research community, and thoroughly demonstrated beyond doubt that CFS is a severe, debilitating physical illness (you don't get major co-infections of retroviruses with a psychological illness). We should use this opportunity to focus research on finding the cause, prevention, and treatments for CFS, regardless of its connection to XMRV.
Before the last XMRV conference, members from the NIH met with CFS patients and offered an avenue for appropriate feedback about our concerns. I think it is appropriate to express our desire to the NIH that they fund a significant research program specifically into the cause and treatment of CFS regardless of its association with XMRV. For instance, wouldn't it be fantastic if someone of the caliber of Ian Lipkin in cooperation with other researchers such as WPI focused their attention on finding the cause of CFS, irrespective of its association with XMRV. If the proposed XMRV association studies prove positive, then great, we don't stop there, but immediately focus on demonstrating causation. More importantly if the association or causation is negative or inconclusive, we don't stop there, anymore than we stopped looking for the cause of AIDS, or SARS, or West Nile virus.