For the second time in a week, a key study suggesting a link between a retroviral infection and chronic fatigue syndrome has been retracted.

A controversial study published in the journal Science in October 2009, which found an association between the illness and a mouse leukemia retrovirus known as XMRV, was retracted last week by the editors of the journal. On Monday, a study that linked the syndrome to retroviruses closely related to XMRV, published in August 2010 by The Proceedings of the National Academy of Sciences, was retracted by its authors.

The second study had provided crucial support to the idea that these pathogens were connected to chronic fatigue syndrome, but other researchers were not able to confirm such an association. Some scientists reported that XMRV itself had been created accidentally during laboratory procedures and that contamination of laboratory materials was widespread.

The authors of the study retracted on Monday included highly respected researchers from the Food and Drug Administration, the National Institutes of Health and Harvard Medical School. Randy Schekman, the former editor in chief of PNAS, said the journal had been “encouraging” the authors to reconsider their findings in light of subsequent research.