How easily can Coryza spread?

[CWitty]

I recently posted about a bird I stupidly bought at a local "farm" this past Sunday. As soon as I got a chance to really look at it after getting home, I realized it was sick. Crusty nose and foul smelling odor. Coryza. Needless to say I have learned a lot since Sunday. At this point I had not had the bird near my 4 buff orps while I could figure out what to do with it. No stomach for culling. I dropped the bird with a woman who is planning to keep it quarantined and treat with meds. and will cull if it gets worse. Anyway, my question now that it's gone, is there any way my birds could have caught whatever it was? Normally I sit and socialize with my flock numerous times a day, but while I had the bird, I changed shoes, changed clothes, scrubbed hands, wore an apron any time I went out to care for my birds with zero social/physical interaction with them like I normally would the whole time the 'visitor' was here, which was 4 days total. Again the sick bird was inside my house in a brooder and my girls roam the yard during the day and cooped at night; never once coming near each other. Maybe I'm paranoid (ok I'm totally freaking out) that I see a small amount of watery (clear) discharge from one of my girls. No other symptoms. Can they simply have a little watery discharge or is it looking like the illness spread despite my efforts? I guess I need reassurance.... or to be prepare for the worst ... I'm so stupid.