The cause of chronic fatigue syndrome, which causes symptoms like profound exhaustion, muscle and joint pain, and cognitive problems, remains unknown, and some researchers have dismissed it as psychosomatic or imaginary, the New York Times reports. Now, a series of announcements have made the issue more confusing than ever for the million or more Americans who suffer from it: on Dec. 14, an advisory panel suggested the U.S. Food and Drug Administration bans blood donations from people with a history of CFS, to prevent the possible spread of viruses that have been linked to it by two high-profile studies. But on Dec. 20, the journal Retrovirology published four papers that suggested those studies’ results may have come from laboratory contamination. The studies reported that people with CRS showed higher infection rates with a virus called XMRV or others in the same category, called MLV-related viruses. But other teams have recently found no connection between CFS and these viruses, generating confusion.