That's a good point, thank you for informing me. And I'm glad your son has recovered.

According to their methods (in the supplementary file), they tested IgG antibodies against the viral capsid antigen (VCA), which, according to them, is the best indicator of prior EBV infection.

They did mention that "In contrast, anti-VCA IgM antibodies, a marker of acute infection, are detectable for only a few weeks and are thus not a good marker of past infection."

But this does mean that they tested for EBV latency rather than persistence. And it remains uncertain how EBV latency and persistence differ in their effects on MS development.