depends on the type of assay used, whether the control was adequate, the trial being retrospective.
JCV is pretty much everywhere. the fact that it showed up in these pts doesn't lead em to conclude that tybsabri was the cause. (although it might be).
i have to think that if this were a particularly well designed and controlled study, then AAN would ahve made it an oral presentation. Also, judging from market's rxn to Tysabrio news (ELN up 11% today), the market didn't think it was a big deal either.