Well most likely (crossing fingers) they're just being very careful. Probably was sterilized, just not to their exact specifications. Doesn't have to be sterile - just disinfected. There IS a difference. There can be "bugs" there with little to no harm - just not infectious pathogens.

HIV is an enveloped virus - pretty easy to knock out with chemicals / heat. Hepatitis comes in 3-forms (A, B, & C)... but most are easily inactivated. ANY disinfection/ sterilization efforts would most likely render the instrument non-contagious even if it's not to their full specifications of sterility. Odds are very much in your favor there's no problem. The person before you would also have to be infected.

Don't know this for a fact, but I'd guess they know the status of the patients they perform colonoscopies and those instruments used with HIV+ and/ or Hep+ patients are rigidly cleaned and sterilized.
Granted someone could be infected and blood tests be ; BUT new tests now detect infections only 2 weeks old or earlier now. And those patients would have very low viral loads.
Hope this helps ease your worries.

Best of luck on the tests.
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David (OFI)