Well...not really. More like segregation.
Many things are airborne...and you tending both sets of birds can carry things over.
Read up on biological/medical quarantine:
BYC Medical Quarantine Article
BYC 'quarantine' search
Have you checked him over real well for mites and/or lice?
Best done well after dark with a strong flashlight/headlight, easier to 'catch' bird and also to check for the mites that live in structure and only come out at night to feed off roosting birds.
Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.
Wipe a white paper towel along the underside of roost to look for red smears(smashed well fed mites).
Part the feathers right down to the skin around vent, head/neck and under wings.
