Infection with syphilis cannot be completely ruled out four weeks after the onset of sexual misconduct or high-risk sex. The first manifestation of syphilis is the chancre, a painless ulcer with cartilaginous hardness that appears at the site of contact. No antibodies to syphilis spirochetes can be detected in blood tests at this time, but active syphilis spirochetes can be observed in dark-field microscopy of the secretions on the surface of the chancre. If the chancre is not treated properly, the syphilis spirochetes will enter the bloodstream along with the lymph, and blood tests can only detect syphilis spirochete antibodies, which takes about 2-3 months, so that syphilis cannot be excluded in four weeks.