adopted cat sick

We currently have 3 cats, 1 older 16 year old, and then 2 cats that
are 1. We lost our 18 year old cat 1-1/2 years ago and was devasted as
he was liek a child. Recenlty we decided to get on a waiting list to
adopt a cat that was the same breed, a maine coon. We found one last
week at the humane society and did the adoption...they told us he was
10 months and in perfect health.

So he got neutered and then we took him home the next day...he wasn't
doign well. We thought maybe he was lathargic from the operation..but
he just kept going down hill. We brought him to the hospital only
after having him for 4 days and he hasn't been home now in 4 days. He
is a mess...herpees, tapeworms, and they think something else is wrong
but haven't done any tests yet.

I am afraid to bring him home and risk getting my other cats sick,
especially the eldest...it wouldn't be fair to risk his life. But then
I feel really bad for this poor cat...who by the way is not even 10
months..he is 2..not a big deal/..just goes to show how many lies the
humane society told us!

Any suggestions to put my mind at ease would be greatly
appreciated...I don't even know when they can let him go home.