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Syphilis is a sexually transmitted infection caused by Treponema pallidum. The organism is a motile, thin spirochete 6 to 20 μm long that has the appearance of a helical coil on dark-field microscopy or immunofluorescence. It is a fastidious organism, with a short life span out of host, and is unable to grow on culture media.


Human beings are the only host. Sexual contact is the predominant form of transmission, although it may also occur via very close physical contact with infected mucosal surfaces. Congenital syphilis may occur transplacentally or by passage through an infected birth canal. Transmission by transfusion has also been documented.

After invasion into the patient, the organism rapidly multiplies and disseminates through the perivascular lymphatics and the systemic circulation. Within 3 to 4 weeks, an inflammatory response occurs at the site of initial inoculation, resulting in the characteristic lesion, the chancre (not present in congenital syphilis). If treatment is not received, secondary syphilis develops with clinical manifestations in the skin, mucous membranes, and central nervous system as part of an inflammatory response. Tertiary syphilis may follow with involvement of any organ system. The host immune response is responsible for many of the clinical findings associated with this infection. Long clinically latent periods are common between stages; the infection may persist through the patient’s lifetime with a variety of clinical manifestations. Syphilis causes significant complications if untreated and facilitates the transmission of human immunodeficiency virus (HIV).

Syphilis rates in the United States had declined steadily from 1990 to an all-time low of 2.1 cases per 100,000 population in 2001, but since then have risen almost annually in all disease forms and in all age, sex, racial, and ethnic groups. In 2015, 23,872 cases of primary and secondary syphilis were reported, a rate of 7.5 per 100,000 population, which is the highest in the United States since 1994. The increase in rates is largely attributed to increased syphilis cases in men having sex with men, but budget cuts in public health services funding and an increase in HIV infection also played important roles.

Congenital syphilis rates in the United States declined from 2008 to 2012 from 10.5 to 8.4 cases per 100,000 live births. However, the number of new congenital syphilis cases increased to 12.4 cases per 100,000 (a total of 487 cases) by 2015.



Children and adolescents who acquire syphilis follow a clinical course similar to adults. In infected children, sexual abuse must be presumed and laws require that a report be made and an investigation take place.

The incubation period is approximately 3 weeks (10–90 days) followed by the appearance of the primary stage, which is characterized by a painless, indurated chancre that appears at the ...

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