Here's something that I've thought about on and off for some time, but since I've never spent any time researching it, it may be completely inaccurate. So, we know that one of the best ways to prevent sickness is by keeping clean... washing our hands thoroughly after using the bathroom, not leaving random food around, etc. Ingesting poop is pretty much going to be a health hazard.
Now, when someone farts and you smell it, usually it smells bad... kinda like poop. Now, does that mean that poop particles actually made it into your nose? If it were the case that the poop particles did not actually leave someone's anus and find their way into your nose, then you wouldn't smell it, right?
Does that mean that farting in public (where others can smell it) can increase the spreading of disease? Or, does it not work that way? Same goes for people that take rather odoriferous dumps in a public bathroom stall... are they affecting the health of others?
Maybe it is not necessary for a particulate to enter your nose for you to smell something, but that just doesn't seem right. Anyone have any answers?