What did the vet say when you brought in the second infected kitty? I would hope that *if* it is something that can pass from cat to cat, he would have told you. I would probably start by checking all their ears for signs of mites or any kind of sores. Perhaps there are ear drops that can be prescribed. Mind you, with 11 cats it may be difficult to know if it's being passed from one to the other. It could be coincidence but I would play it safe and get the vet involved in a big way before it gets out of hand. It could get very expensive.