If you take public transport, you are inevitably exposed to a multitude of bugs. Bus door handles, supportive rails, arm rests and the seats are all full of bugs thanks to being handled by many people. Each person brings along some bugs, and deposits them wherever they touch. Then you come along and pick some, and deposit some of your own as well.
Over-diagnosis refers to making a diagnosis that is ultimately not necessary, because the patient would never have suffered any symptoms or death from the said diagnosis.
Over-diagnosis usually occurs when you get screened for a disease, such as cancer, in an effort to detect it at an early stage when it may be more amenable to treatment and cure.
If you suspect you have an STI, you shouldn’t waste any time wondering what to do. You should go straight to a sexual and reproductive health specialist, or to a gynecologist, or indeed to general practitioner and get a thorough assessment.