The bacterium that causes syphilis, Treponema pallidum subsp. pallidum, can be present in semen at high enough concentration to transmit the disease.
“Expedited partner therapy” is recommended, bu many doctors aren’t taking the advice because of entrenched ethical and legal concerns.
Most patients with an STD get treatment only for their own infection — when they probably could get antibiotics for their partner at the same time.
Oregon’s Clackamas County, health officials are asking patients with an STD who their sexual partners are — and then are tracking those partners down.