~141 ..once cleared of virus; on a retest: it was B a a c k .

1) Re-infection?
2) Some aspect of virus, a subtle 'place-marker' remains? (a fault in Testing or ..?)
3) 'Immunity' thus-far, is temporal-by-virus-design? (related to 2) both ways.

The query obviously is just beginning, so maybe none-of-above can be evaluated before, as you note:
[Much] more Testing ... in the millions.
Ya can't make predictions or even Stats, from iggerance. Just as in Politics, War-on-truthiness vs lying-agitprop.

Humans! ..they can't even trust themselves.