Several years ago I used to volunteer for the local SPCA and
fostered cats (where I got Shamrock - he was a foster failure).
Several of the volunteers would at times have at least 100 cats in
their homes.  I thought they were nuts, but after a while I could
understand why it happened.

The worst case I had any participation in was one 4th of July
weekend where I cat sat for one of the volunteers who had a 5000 sq
ft house, and at the time had about 120 cats, 60+ were kittens,
some very very small, and not old enough to be adopted out yet. At
the time there was a nasty strain of feline panleuk ("distemper")
and other nasties going around. I had to dropper feed about 20
kittens to boost appetite, "steam" all of the kittens in the
bathroom to help them breathe, clean butts, medicate with
antibiotics and interferon 2x per day, and make sure everyone ate,
and clean out a whole lot of litterboxes. This was only for 4 days.  
I don't know how those who do this do it.  I quit volunteering soon
after because many died, and no one seemed to care that it was too
much work for those who took it on.  I saw too much suffering. If
there aren't enough foster homes for the sick ones, put them down
before they have to suffer the illness. I'm sure many disagree with
me about that.