A new US study heaps further doubt on the theory that Chronic Fatigue Syndrome is linked to the XMRV retrovirus by questioning the results of a well-known October 2009 report.

That report, which found that patients with CFS were often infected with the virus, was published in the prestigious journal Science and attracted a lot of attention, but subsequent studies have failed to replicate the results.

The new study, published Thursday and based on the findings of researchers at nine different laboratories, including the authors of the original report, found that the lab tests used to detect the retrovirus were unreliable.

The researchers analyzed blood samples from 15 people previously reported to be infected with XMRV or a related virus and 15 healthy individuals.

The samples were "blind-coded," meaning the labs did not know which samples they were testing.

"Only the two laboratories associated with the original report detected the virus," said a summary of the new study published by Science.

"In these two labs, the virus was found in healthy controls as often as in the CFS patients, and tests on replicate samples... produced inconsistent results," raising major doubts about the original report.

The US Centers for Disease Control and Prevention describe CFS as a "devastating and complex disorder characterized by overwhelming fatigue that is not improved by bed rest and that may be worsened by physical or mental activity."