One of the things I learned as a student, during my many years of summer jobs at the local sewage farm, was that those pesky germs are all around us, every day, and that it's a testament to our genetic resilience that we survived the last 100,000 years or so without all being wiped out by a random sneeze, or a cough, or a violent and unfiltered fart. If we hadn't been that tough, then our species would have been wiped out long ago by our every dalliance with the lower torsos of our fellow humans, including sex (obviously).
That's the beauty of antibodies, innit? They say that you need to ingest ten billion hostile bacteria to stand any real chance of getting ill. And that, even then, the 100
trillion bacteria in your gut will probably make short work of the invaders before they have the opportunity to do anything really nasty to you.
As for my boss at the sewage farm, he had his own favourite test that showed him whether or not the secondary-stage sewage on the tanks (about two weeks old) was ready to be moved on to stage three. He would dip his finger in and taste it. The last I heard, he was still alive.
BJ