So I did some research and came across this: Transmission of Infection by Flexible Gastrointestinal Endoscopy and Bronchoscopy. It seems that there's little evidence for infections and that the evidence indicates otherwise, namely, that the rate of infection is extremely low. However, as the article notes, that could very easily be due to lack of clinical symptoms and lack of surveillance. And it turns out that you can't sterilize but only disinfect the scope. So it's worth considering this risk, it seems even if the evidence isn't there, because the data collection if weak. Though one reason for the the lack of clinical data/symptoms could be that the body fights off any such infection or that there aren't that many infections. It's just so difficult to tell without good date and that's unavailable it seems.