Definitely a legitimate question. Though the likelihood of a diver having active TB is pretty low, there are other much more common diseases that can be transmitted by sharing a regulator. Norovirus comes to mind right away, only because I was just reading about it this morning. If someone else has used your regulator and you're truly concerned about disease transmission, a 20-second immersion a 10:1 water:bleach solution kills just about everything. Make sure you rinse the regulator thoroughly with running water afterward as any remaining bleach could have corrosive effects on regulator parts. During training, if your buddy appears ill or has obvious signs like a cough or runny nose, it's reasonable to politely decline to share a regulator with him/her.
