Has this condition been diagnosed in any nation other than the US? That seems like very relevant information. Don’t recall that being answered in several previous articles on this subject.
I believe that it is native to Central America.
Freeper "trebb" did further research on 12/18/18 and found:
" A71 - First identified in the United States in 1969, enterovirus A71 (EV-A71)
is one of more than 100 non-polio enteroviruses.
Worldwide, EV-A71 is a common cause of hand, foot, and mouth disease in infants and young children."
The paralysis occurs as the virus attacks the lining of the nervous system, and then seems to disappear,
thus not being found in spinal fluid of patients , most of whom are youth.
That is part of the mystery of this illness - sometimes it remains,
and sometimes it can't be found to conclusively correlate the virus to the paralysis.