Health Advisory: Increased Incidence of HIV and Syphilis Co-Infection Among Missourians of Child-Bearing Potential

From 2020 through 2022, there were 56 cases of congenital syphilis reported in St. Louis County and the City of St. Louis.

November 2, 2023 | 3 min reading time

A marked increase in syphilis in people of childbearing potential has driven rising rates of congenital syphilis (CS). Syphilis and HIV co-infection among pregnant patients can also increase the risk of HIV vertical transmission. All cases of CS and HIV vertical transmission can be prevented with increased testing and appropriate treatment. Vertical transmission is where viruses can pass between mother and baby in utero.


In 2021, 63 congenital syphilis cases were reported in Missouri, representing the highest number of cases reported since 1994. Congenital syphilis occurs when syphilis is transmitted from mother to baby during pregnancy and can cause miscarriage, stillbirths, infant death, and long-term disability. Each CS case is completely preventable with timely maternal syphilis testing and treatment. From 2020 through 2022, there were 56 cases of congenital syphilis reported in St. Louis County and the City of St. Louis. This is more cases than in the previous 20 years combined (47 cases in 1999-2019).

Amid the uptick in congenital syphilis cases, there is also an increased incidence of perinatal HIV transmission documented in Missouri as well as pregnant people co-infected with syphilis and HIV. Among pregnant patients who are HIV positive, the risk of vertical transmission is much higher with concurrent syphilis infection. (1) However, each vertical case of HIV transmission is also completely preventable with appropriate testing and treatment. 

  1. A sampling of studies demonstrating increased risk of vertical HIV transmission: 

    "Mothers co-infected with HIV and syphilis had twice the odds (AOR 2.1, 95% CI 1.3-2.4) of transmitting HIV infection to their babies. Of the 1684 infants born to 1664 mothers enrolled in the NICHD/HPTN 040 (P1043) trial, 24 (1.4%) were co-infected with HIV and syphilis, and of these infants, 21 (88%) acquired HIV infection in utero. Among the 116 infants infected with HIV whose mothers did not have serological evidence of untreated syphilis infection, 62% of them acquired HIV in-utero." DOI: 10.1097/INF.0000000000000578

    "In this present study, 8.3% of the children of HIV/Syphilis co-infected mothers were infected by the virus, this being a value 4 times higher than the stipulated for the country, and more than 10 times higher than the rate of vertical transmission of HIV-positive mothers without syphilis during pregnancy, whose rate was 0.77% in this study." DOI:10.25060/residpediatr-2021.v11n1-141


  • Providers should routinely test pregnant patients for syphilis three times during pregnancy—at the first prenatal care visit, in the third trimester at 28 weeks, and at delivery—to identify and treat syphilis to prevent congenital syphilis. 
  • Providers should routinely test pregnant patients for HIV.
  • Providers should routinely test people living with HIV for syphilis, especially pregnant patients, due to increased risk of perinatal HIV transmission from HIV / syphilis co-infection. Individuals who are co-infected should receive testing and treatment to prevent vertical transmission of HIV.
  • Any point of contact with the healthcare system (emergency departments, urgent cares, sick visits) may be the only interaction with health providers for different patient populations. Increasing HIV and syphilis testing during these visits may help address missed opportunities for care for confirmed pregnant patients. 
  • Providers with questions about management of perinatal HIV exposure should consult an expert in pediatric HIV infection or the National Perinatal HIV hotline (1-888-448-8765), which provides free clinical consultation on all aspects of perinatal HIV, including newborn care. Perinatal HIV management guidelines are also available online at:
Treatment Table
Treatment Population Stage Treatment
Syphilis during pregnancy Primary
Early non-primary
2.4 million units of IM benzathine penicillin G (1)
  Unknown duration
Benzathine penicillin G 7.2 million units total, administered as 3 doses of 2.4 million units IM each at 1-week intervals (2)
  Neuro, ocular, and otic syphilis Aqueous crystalline penicillin G 18-24 million units per day, administered as 3-4 million units IV every 4 hours or continued infusion, for 10-14 days
Congenital syphilis in the infant (3)   Aqueous crystalline penicillin G 100,000-150,000 units/kg/day, administered as 50,000 units/kg/dose IV every 12 hours during the first 7 days of life and every 8 hours thereafter for a total of 10 days 
Procaine penicillin G 50,000 units/kg/dose IM in a single daily dose for 10 days
  1. Patients with penicillin allergies should be desensitized and treated with penicillin as it is the only known effective antimicrobial for preventing maternal transmission to the fetus and treating fetal infection. 
  2. If doses are further apart than 9 days or missed, the treatment schedule must restart from the beginning. 
  3. Treatment recommendations for congenital syphilis differ based on CDC case scenario; expert consultation is available for management questions. If more than 1 day of therapy is missed the entire course should be restarted.

Additional Resources

Missouri DHSS - Congenital syphilis Health Alert Note:

STI Treatment guidelines:
Syphilis Pocket guide:

National Network of Prevention Training Centers - Clinical consult website:

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