Two months ago I wrote about two contradictory studies on the presence of the novel XMRV retrovirus in blood of patients with Chronic Fatigue Syndrome (CFS).
The first study, published in autumn last year by investigators of the Whittemore Peterson Institute (WPI) in the USA , claimed to find XMRV virus in peripheral blood mononuclear cells (PBMC) of patients with CFS. They used PCR and several other techniques.
A second study, performed in the UK  failed to show any XMRV-virus in peripheral blood of CFS patients.
Now there are two other negative studies, one from the UK  and one from the Netherlands .
Does this mean that XMRV is NOT present in CFS patients?
No, different results may still be due do to different experimental conditions and patient characteristics.
The discrepancies between the studies discussed in the previous post remain, but there are new insights, that I would like to share.