D.K.
It doesn't matter where he got it, it is a very common childhood thing to get. Once the rash appears they are no longer contagious from what I understand. It isn't anything you can prevent. It is very common, don't worry too much. If it is fifths disease he will have immunity to getting it again.
Is fifth disease contagious?
Yes. A person infected with parvovirus B19 is contagious during the early part of the illness, before the rash appears.
By the time a child has the characteristic "slapped cheek" rash of fifth disease, for example, he or she is probably no longer contagious and may return to school or child care center. This contagious period is different than that for many other rash illnesses, such as measles, for which the child is contagious while he or she has the rash.