XMRV is transmitted through bodily fluids such as semen, blood and breast milk, according to the Whittemore Peterson Institute for Neuro-Immune Disease.
In the new study, researchers took fresh blood samples from 15 people who had previously tested positive for XMRV or a related virus (14 of them had CFS), and 15 people without CFS who had previously tested negative for the virus.
Nine different laboratories, including two that were involved in the 2009 report, then tested the samples in a blinded fashion, meaning they didn't know which specimens were which.
The only labs to detect XMRV were the two from the original study and, even then, they found the virus just as often in people with CFS as in healthy controls.
One lesson to be learned from this, said study senior author Dr. Michael Busch, is that "we really do need to create blinded panels and validate the performance of tests before they get employed in larger studies so people aren't misled from early data from assays that aren't accurate."
The partial retraction from two authors of the 2009 paper conceded that some of the original blood samples were contaminated, but they stood by the rest of their research.
Although this latest report leaves the quest to find the cause or causes of CFS back where it was in 2009, the upside is that even the negative findings have stirred interest in the disease.
"I think the renewed interest and focus on CFS is good," said Busch, who is director of the Blood Systems Research Institute and a professor of laboratory medicine at the University of California, San Francisco. "There is a lot of research that is going on."
The U.S. National Institutes of Health is sponsoring additional research on XMRV and chronic fatigue syndrome.
"The story doesn't end here. There are many impo
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