I am surprised at people who foster without a separate room to keep them in - it isn't just the risk of transmitting diseases, there is the temperaments of the cats and the constant comings and goings that could stress your own cats - what would you do if you got a cat that really hated other cats, they could attack one of your own cats? I keep mine isolated for the first two weeks in case of illness and so I can see them on their own and assess their personality. They then get an hour or so out of their room to see what they are like with other cats, but that is it, as it is my cats home and I dont want them having to constantly deal with all these cats. I did used to do things slightly different, they used to get more time out, but I currently have a long term foster who hates cats, plus I have the foster with calici. The only time I do things different to that is if i have either a long termer due to age or a terminally ill cat, they will get slowly integrated (although the three terminally ill cats this year still had a lot of time in their own room for varying reasons).