Or there is an underlying husbandry problem which is allowing it to resurface. Most bacteria is on us/environment all the time, just our immune systems fight it off unless it becomes compromised. Same goes with animals but yes, if after 2 months it still has RI, then you got bigger issues and you need to re evaluate husbandry and why you would have an animal on baytril for 2 months straight is an even bigger question.