As you stated, “Skin to skin contact” is all that is needed.
That would mean Passenger A infecting TSA agent by skin to skin contact, then TSA agent passing it on to Passenger B by skin to skin contact.
Do you have any evidence that his happens?
I suspect that this form of transmission would be even rarer than female to male HIV transmission.
Well, considering that the process of drying actually kills a *lot* of bacteria/viruses it’s highly likely it would have to happen before the sweat evaporates.
That said, I have no wish to “try my luck” on that.
PS - You only asked if there was an STD which could be spread by skin-to-skin contact; I have provided one case for you — the answer is YES.