I'm getting over an MG outbreak at my place. The best thing i did was to STOP medicating. I tried for months to get rid of it, and when I stopped trying, it cleared up. I had one loss. I've really come to the conclusion that not medicating is the way to go (for ME, not everyone) with outbreaks. The ones that make it develop a resistance to it, and the ones that don't.. well they were just going to continually get sick. By letting it run it's course, i've built up the strength of the flock in general. It may seem harsh, but it's what worked for me. I noticed the beginnings of it right after hurricane Ike (I remember because I was outside burning brush when I heard the first sneeze.), and i'm just NOW getting it gone. I have one sussex that's still snotty. Everyone else is completely back to normal.
To everyone that has to deal with it, good luck. It sucks like nothing you've ever seen, but it's inevitable. MG is absolutely everywhere.