Thank goodness Ela .. quick question do your fosterers keep the fosters in a seperate room? I have a reason for asking
It is not wise to mix cats from different situations, a little different if you are adopting a cat and you already have one, as hopefully your cat is healthy and the cat you have adopted has been health checked and been in care a while to be assessed. Although even when someone adopts a cat from us and they already have a cat we suggest they are kept separate for a while and introduced gradually.
Also when a cat re-homed it is sometimes a time of stress and if stressed a cat may bring out something it was perhaps incubating but would have not otherwise come out.
When a foster cat comes in you often have no idea if it has anything wrong with it so there are potential health risks to your cats, also as advised on another topic if we all had our own cats tested for certain things many of us would perhaps have a nasty shock. So your cats may be a risk to the foster cats whose immune system is not as strong as it could be, (actually I know mine are OK as they have been tested over the years due to mouth problems and they have not mixed with other cats).
If a fosterers own cats came down with something that it was thought a foster cat had bought in can you imagine the number of claims against rescues.