Congenital Syphilis in the US: Cases, Causes & Prevention

Congenital syphilis happens when syphilis passes from a pregnant person to the fetus through the placenta or during birth. US cases have surged from 2,163 in 2020 to 3,882 in 2023 CDC AtlasPlus, 2023 — the highest level in decades. It's almost entirely preventable with prenatal screening and penicillin treatment of the mother.

The numbers: how bad is it?

This is one of the fastest-moving crises in US public health. Congenital syphilis nearly doubled in four years, rising about 79% from 2,163 cases in 2020 to 3,882 in 2023. The increase tracks almost perfectly with a broader explosion of syphilis among adults: there were roughly 53,000 primary-and-secondary cases nationally in 2023, and the late or unknown-duration stage jumped from about 14 to nearly 30 per 100,000 between 2020 and 2023 CDC, 2023.

The burden isn't spread evenly. In 2023 the national primary-and-secondary rate was 15.8 per 100,000, but several states ran far higher — South Dakota at 73 per 100,000, Washington DC at 40, New Mexico at 37, and Mississippi at 30. Because adult and infant syphilis move together, the places with the worst adult numbers tend to see the most congenital cases. You can see how your area compares in our breakdown of STD rates by state.

What is congenital syphilis — what happens to the baby?

Congenital syphilis is what we call it when the bacterium Treponema pallidum crosses the placenta into the developing fetus, or infects the baby during delivery. The spirochete travels through the bloodstream and can take hold in nearly any organ system, which is why the damage it causes is so varied and so serious.

The earliest consequences can be catastrophic before a baby ever takes a breath: stillbirth, premature birth, low birth weight, or a severely ill newborn. The cruel part is that many infected infants look completely normal at birth. The infection smolders, and problems surface months to years later — which is exactly why an infant whose mother had untreated or inadequately treated syphilis is evaluated, treated, and followed even when the baby seems healthy CDC pregnancy guidelines.

When congenital syphilis goes untreated or is treated late, the long-term toll can include:

• Deafness — damage to the hearing nerves, sometimes appearing in later childhood.
• Blindness or eye damage from inflammation inside the eye.
• Bone and joint damage that can deform the developing skeleton.
• Neurological damage, including developmental delays and seizures from infection of the central nervous system.
• Death — in the most severe untreated cases.

Why are cases surging?

Congenital syphilis is downstream of adult syphilis, and adult disease has been climbing relentlessly. The surge in infants mirrors a sharp rise in primary-and-secondary syphilis among women of reproductive age since 2015 — more pregnant people are entering pregnancy already infected, or catching it during pregnancy.

But infection alone doesn't have to reach the baby — the system is supposed to catch it. The surge reflects where that system breaks down: limited access to prenatal care, so some people are never screened in time; inadequate testing coverage in the highest-burden communities; drug use, which correlates strongly with delayed or absent prenatal care; and lapses in partner treatment, where a treated patient gets reinfected because their partner wasn't treated. Each of those is a missed chance to stop a preventable infant infection.

Who is most at risk?

The single biggest risk factor isn't a demographic — it's missed or late prenatal care. People who don't see a clinician early in pregnancy, who change providers without records following them, or who face barriers like housing instability or substance use are far more likely to slip through. Geography matters too: living in a high-prevalence area raises the baseline odds of exposure.

A common and dangerous assumption is "I'm not at risk." Syphilis has spread well beyond historically high-risk groups, and partner status can change in ways a pregnant person doesn't know about. That's why screening guidance doesn't ask anyone to self-assess — every pregnant person is screened regardless of perceived risk.

How is it prevented?

Prevention rests on two simple steps done on time: screen the mother, then treat her. The USPSTF gives a Grade B recommendation to screen all pregnant persons for syphilis at the first prenatal visit, and to rescreen at 28 weeks and again at delivery in high-prevalence areas or at-risk populations USPSTF, 2023.

The screen itself is undramatic — a routine blood test (RPR or VDRL) drawn as part of the standard first-visit prenatal panel. It's quick and you won't notice it among the other labs. A positive result is confirmed with a second, treponemal-specific blood test before any treatment decisions are made. If you haven't had recent testing and want it outside of prenatal care, you can get tested first.

Treatment is where syphilis becomes uniquely fixable in pregnancy: benzathine penicillin G is the only proven drug that reliably crosses the placenta to treat the fetus. The dose follows the stage — one injection (2.4 million units) for early syphilis, three weekly injections for late or unknown-duration disease StatPearls. There is no oral drug that dependably substitutes, and crucially, no alternative antibiotic is proven safe and effective for preventing congenital syphilis. Treatment is most protective when it begins early enough before delivery — ideally at least 30 days — to give the fetus time to clear the infection.

What about a penicillin allergy? Most penicillin allergy is mislabeled — over 90% of people who think they're allergic actually aren't. A pregnant patient with a true allergy is desensitized to penicillin and then treated with it, rather than given a weaker drug, because nothing else protects the baby. For the full picture of stages, timing, and follow-up, see our syphilis in pregnancy guide.

What happens if it's missed?

Untreated syphilis in pregnancy harms the baby in 50 to 80% of cases — stillbirth, prematurity, newborn death, or congenital infection. Those aren't worst-case outliers; that's the central tendency when the infection goes unaddressed WHO. Syphilis also roughly doubles the risk of acquiring HIV, which compounds the danger for both mother and baby.

A note for any pregnant person already being treated: cure is confirmed by blood titers, not by feeling better. A fourfold drop over 6 to 24 months (say 1:32 to 1:8) means treatment worked; a fourfold rise signals reinfection or failure and prompts retreatment. And syphilis can invade the eyes or nervous system at any stage — ocular and neurosyphilis aren't only late complications, so new vision changes or neurological symptoms in someone with syphilis are a medical emergency StatPearls.

Current CDC recommendations for pregnant people

The standing guidance is straightforward and, followed fully, would prevent nearly every case:

• Screen for syphilis at the first prenatal visit, for every pregnant person.
• Rescreen at 28 weeks and again at delivery in high-prevalence areas or at-risk populations.
• Treat any positive case with stage-appropriate benzathine penicillin G — and desensitize rather than substitute if there's a true penicillin allergy.
• Treat the partner so the patient isn't reinfected.
• Evaluate, treat, and follow every infant born to a mother with untreated or inadequately treated syphilis, even if the baby looks well at birth.