Syphilis is usually contracted through sexual contact. The presence of treponemes in the genitals of contactees or places of their usual residence is called carriage. It is most often detected during re-examination of a sexually active partner 3 weeks after sexual intercourse. Primary infection occurs. The sooner the examination occurs after contact, the greater the chance of identifying carriers, men with primary syphilis. If the period from contact to examination was greatly extended, then the proportion of primary cases increases. After unprotected sexual intercourse, the risk of infection is high for a duration of 2 hours to 5 days. With longer contacts the risk decreases.
When signs of the disease appear, the source of infection is often a woman, especially with primary and secondary forms of syphilis. About a quarter of all cases of infection are caused by the so-called household route - through injured skin, cuts, burns.