Bantam hen with cholera...what to do and with others in flock?

[jsjustice7]

I'm a newbie. I bought hens (2 RIR and 1 Barred Rock)to get started. A few days later they came down with cholera. I went bought some medicine at our local co-op. They got better. About a month later, I got 5 (Bantams) more hens. Its been about 2 1/2 weeks. One of the bantams has came down with it too. I don't know what to do. Should I take out the sick one and just treat it or should I go ahead and treat them all even though they aren't showing signs yet? I guess I probably need to sanitize the whole chicken co-op but to do with chickens in between time? Help.

Thanks,
Sandra in AL