The Sleep Education Blog reported on the previous research in October. The U.S. study identified DNA from the “XMRV” virus in the blood of 68 out of 101 people with CFS.
The new study was conducted in the U.K. DNA was extracted from blood samples of 186 people with CFS. They were screened for the XMRV virus and for another closely related virus.
Results published on Wednesday show that neither virus was detected in any of the samples. The authors suggested that the results may be a result of population differences between North America and Europe.
“We used very sensitive testing methods to look for the virus,” study co-author Myra McClure said in a news release. “If it had been there, we would have found it. We are confident that our results show there is no link between XMRV and chronic fatigue syndrome, at least in the U.K.”
But the institute behind the U.S. research questioned the methods of the U.K. study.
“This study did not duplicate the rigorous scientific techniques (used by the U.S. research team),” said a group statement. “Therefore it cannot be considered a replication study… Significant and critical questions remain as to the status of patient samples used in the U.K. study.”
Simon Wessely, another co-author of the U.K. study, also cautioned that their results are not conclusive. He said more research is needed to determine the fundamental cause of CFS.
"It is important to emphasize that today's findings do not invalidate all previous research,” said Wessely. “As ever in science, no single study is conclusive.”
CFS occurs four times more often in women than in men. The CDC notes that CFS is neither a form of depression nor a mental illness.
“There is now abundant scientific evidence that CFS is a real physiological illness,” reports the CDC. “A number of biologic abnormalities have been identified in people with CFS.”
One common symptom of CFS is unrefreshing sleep. This can make it hard to distinguish the syndrome from a group of sleep disorders known as “hypersomnias.”
Read more about hypersomnia.