http://www.ncbi.nlm.nih.gov/pubmed/22842604 New Microbiol. 2012 Jul;35(3):341-4. Epub 2012 Jun 30. Xenotropic and polytropic murine leukemia virus-related sequences are not detected in the majority of patients with chronic fatigue syndrome. Paolucci S, Piralla A, Zanello C, Minoli L, Baldanti F. S.S. Virologia Molecolare, S.C. Virologia e Microbiologia, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy. XMRV and polytropic MLV-related virus have been controversially associated with chronic fatigue syndrome (CFS). Subsequent reports failed to detect XMRV and MLV-related virus in CFS patients, and the previous results have been interpreted as a massive laboratory contamination by mouse DNA sequences. Among 12 sequential CFS patients, two were positive for XMRV/MLV sequences. In contrast, 40 selected control subjects were negative. CSF patients and controls were negative for mitochondrial mouse-specific DNA sequences. These findings do not confirm the high frequency of MLV-related viruses infection in CFS patients, but also contrast the widespread laboratory contamination previously suggested.