the point is they are never actually touching your skin
they are only patting down outside your clothes
there is no way to transfer any pathogen from these pat downs
Really? Why do hospitals disinfect sheets? Why do doctors always wash their hands after seeing a patient, even if they did not touch the patient? Disease vectors are a lot more persistent than skin to skin contact.
If a person has an infectious disease, sneezes into their shirt sleeve, and gets patted down by the TSA, those germs can be transferred to the gloves they are wearing, then to your clothing. When you take those clothes off it can transfer to your hands, and thus you.
Just because something is classified as an STD, that does not mean the sex is the only vector that transmits that disease. It is just one of them, possibly the most convenient for that pathogen.