You're shedding about 15 million bacterial cells into the immediate environment around you every minute. Those 15 million cells comprise mostly of bacteria associated with skin, but they also come from your nose and your mouth, and interestingly, even from your gastrointestinal system via your trousers and on to these seats you're sitting on. So, you leave a signature wherever you go. And those bacteria land on the surface, most of them die, but some of them go dormant or they proliferate, then they can be transmitted from you to another person.
Which means if we were in a hospital and another person comes into that part of the hospital where someone with a certain type of bacteria has been, there is, therefore, the prospect for them to pick up those bugs.