Correct, however this could be a fault with the test rather than no XMRV present (e.g.a false negative).
The WPI PCR XMRV test took 4 to 5 goes to find people positive, for example. Is the Alter/Lo method as sensitive as the WPI or better?
We don't know. Was the person negative for XMRV tested also by virus culture method? That would be very interesting to know actually.
We still don't have a FDA approved standardised test or know where the virus reservoir is. It may migrate into tissue (s). It may be expressed at levels so low it cannot be detected by current assays in some people. (From memory XMRV is approximately 1 in 1 million cells infected, and HIV is 1 in 1,000 cells infected)
NB: In Ila Singh's research monkeys injected with XMRV, the virus also escaped from the blood and could not be detected.