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Syphilis is a sexually transmitted infection caused by Treponema pallidum, which is a thin, motile spirochete that is extremely fastidious, surviving only briefly outside the host. According to the Centers for Disease Control and Prevention (CDC), a case of congenital syphilis (CS) is defined as illness in an infant from whom lesional, placental, umbilical cord, or autopsy material specimens demonstrated T. pallidum by dark-field microscopy, fluorescent antibody, or other specific stain; an infant whose mother had untreated or inadequately treated syphilis at delivery (ie, any nonpenicillin therapy or penicillin administered <30 days before delivery); or an infant or child who has a reactive treponemal test for syphilis and any of the following: evidence of CS on physical examination, evidence of CS on radiographs of long bones, reactive cerebrospinal fluid (CSF) venereal disease research laboratory test (VDRL), elevated CSF cell count or protein (without other causes) or a reactive fluorescent treponemal antibody absorbed–19S-immunoglobulin M (IgM) antibody test or IgM enzyme-linked immunosorbent assay. This definition includes infants who are stillborn to women with untreated syphilis.
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The incidence of CS parallels that of primary and secondary syphilis in the general population. The most recent incidence in the United States is 10.1 cases per 100,000 live births, which represented an increase of 23% between 2003 and 2008. Rates of infection remain disproportionately high in large urban areas and in the southern United States. Worldwide, syphilis continues to represent a serious public health problem with a recent increase in incidence documented in both the developed and underdeveloped world. The World Health Organization estimates that 1 million pregnancies are affected by syphilis worldwide. Of these, 460,000 will result in stillbirth, hydrops fetalis, abortion, or perinatal death; 270,000 will result in an infant born preterm or with low birthweight; and 270,000 will result in an infant with stigmata of CS. The rate of CS is increased among infants born to mothers with human immunodeficiency virus (HIV) infection.
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Treponemes are able to cross the placenta at any time during pregnancy, thereby infecting the fetus. Syphilis can cause stillbirth (30–40% of fetuses with CS are stillborn), preterm delivery, congenital infection, or neonatal death, depending on the stage of maternal infection and duration of fetal infection before delivery. Untreated infection in the first and second trimesters often leads to significant fetal morbidity, whereas with third-trimester infection, many infants are asymptomatic. The most common cause of fetal death is placental infection associated with decreasing blood flow to the fetus, although direct fetal infection also plays a role. Infection can also be acquired by the neonate via contact with infectious lesions during passage through the birth canal. Kassowitz's law states that the risk of vertical transmission of syphilis from an infected, untreated mother decreases as maternal disease progresses. Thus transmission ranges from 70–90% in primary and secondary syphilis, to 40% for ...