Syphilis (SIH-fuh-lus) is an STI caused by a thin, corkscrewlike bacterium called Treponema pallidum (also commonly called a spirochete).

Incidence and Transmission

Syphilis rates declined steadily in the United States throughout the 1990s (Rosen, 2006). Unfortunately, syphilis rates have recently risen. This overall increased inci­dence of syphilis was largely attributable to an increase among men who have sex with men (MSM) (Mayer & Mimiaga, 2011).

Treponema pallidum requires a warm, moist environment for survival. It is trans­mitted almost exclusively from open lesions of infected individuals to the mucous membranes or skin abrasions of sexual partners through penile-vaginal, oral-genital, oral-anal, or genital-anal contacts.

An infected pregnant woman can also transmit Treponema pallidum to her unborn child through the placental blood system. The resulting infection can cause miscarriage, stillbirth, or congenital syphilis, which can result in death or extreme damage to infected newborns (Centers for Disease Control, 2010a; Hawkes et al., 2011). Worldwide more than 2 million pregnant women have active syphilis (Hawkes et al., 2011), and every year at least 500,000 children are born afflicted with congenital syphilis (Ramiandrisoa et al., 2011). If syphilis is successfully treated before the 4th month of pregnancy, the fetus will not be affected. Therefore pregnant women should be tested for syphilis some­time during their first 3 months of pregnancy. The CDC recommends that all pregnant women be tested for syphilis at the first prenatal visit.


A raised, red, painless sore that is symptomatic of the primary phase of syphilis.