upper respiratory infection question on chickens

[chickencharm]

I have a question about my Silkies that got that upper respiratory infection. I bought some SL50 antibiotic and put them on it and they are getting better now. My question is once they are all free of runny noses and sneezing, can i still sale them, and if so how long do i need to wait after they are better to make sure they arent going to be carrier's. i do not want to make other peoples chickens sick too.
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