I'm not so sure about that. It might seem unlikely in this case, but I can give you a list of conditions a mile long where the sensitivity and specificity of the various testing methodologies changes substantially based on the point in the illness, the organs effected, etc... It wouldn't be unheard of for a pathogen to be more active based on when it is tested for or under what conditions. For example (pure speculation) - if XMRV is so triggered by cortisol, perhaps it would be better to test for it in the early AM, when the body's production of cortisol is the highest. Same with androgen hormones, perhaps women have higher blood levels at certain points in their cycle. Or perhaps the levels in the blood would go up during exercise? The only way to find out is to run an experiment. Bottom line.. before XMRV is dismissed or endorsed, someone needs to run an experiment to connect the dots and explain the discrepancies in the studies. Everything else at this point is just conjecture.