Clinical Pearls & Morning Reports

Posted by Carla Rothaus, MD

Published January 17, 2024


What are some of the challenges to the elimination of congenital syphilis?

Congenital syphilis usually results from transplacental passage of Treponema pallidum to the fetus during disseminated maternal infection. Read the NEJM Review Article here.

Clinical Pearls

Q: What patterns have been observed in recent decades regarding rates of syphilis in the U.S.?

A: After a steady decline in U.S. cases of primary and secondary syphilis after 1990, which led to hopes of its elimination, rates hit a nadir in 2001. Unfortunately, the rates have subsequently increased among men and women of reproductive age, as well as infants, and in 2021, the rate of congenital syphilis in the United States was the highest it has been in nearly 30 years.

Q: In a pregnancy complicated by syphilis, what is the risk to the fetus of congenital infection?

A: The risk to the fetus of congenital infection is 50 to 70% in pregnancies complicated by early syphilis but decreases to 15% if maternal syphilis was contracted more than a year before the pregnancy. Transmission may occur at any time during pregnancy, and the risk of transmission is thought to increase with the duration of gestational exposure.

Morning Report Questions

Q: How is a fetus assessed for evidence of congenital syphilis?

A: The sensitivity of dark-field microscopy for visualizing T. pallidum in samples from amniocentesis ranges from 42 to 86%, but dark-field microscopy remains impractical because of its limited availability. Direct fluorescence antibody testing for T. pallidum is not available in the United States. Nuclei acid amplification testing has a sensitivity ranging from 75 to 100%. Given the limited sensitivities of dark-field microscopy (when available) and nucleic acid amplification testing, ultrasonography is the most commonly used method to examine a fetus for evidence of congenital syphilis. Ultrasonographic evidence of intrauterine infection, which can be detected after 18 weeks of gestation, when the fetus is able to mount an immune response to T. pallidum infection, includes fetal hepatomegaly (in 80% of cases); anemia, as indicated by the peak systolic velocity of the middle cerebral artery (33%); placentomegaly (27%); polyhydramnios (12%); and nonimmune hydrops (10%). However, the absence of ultrasonographic abnormalities does not rule out congenital infection. The prevalence of congenital syphilis at delivery ranges from 12 to 15% among at-risk fetuses with no ultrasonographic findings of congenital infection.

Q: What are some of the challenges to the elimination of congenital syphilis?

A: Persistent challenges to the elimination of congenital syphilis include structural health care barriers that may be compounded by mental illness and substance use. Fear of legal or punitive actions resulting in loss of child custody perpetuates barriers to prenatal care among women who struggle with substance use disorders. Despite increased efforts to improve syphilis testing and treatment, strategies to improve treatment of sexual partners are failing. The risk factors associated with lack of an appropriate syphilis diagnosis and follow-up for mother–infant dyads have been the focus of CDC-supported and other federal, state, and city intervention efforts. New initiatives include implementation of opt-out screening at the time of pregnancy testing, including in the emergency department and at urgent care centers, and rapid syphilis testing with presumptive treatment if the result of an isolated treponemal-specific test is positive or if the physical examination and symptoms are suggestive of syphilis.

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