Syphilis

What Syphilis Is

Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum. It spreads through direct contact with a syphilitic sore during vaginal, anal or oral sex. It can also spread through kissing when oral lesions are present and from mother to baby during pregnancy or delivery. Syphilis can infect multiple body systems and, without treatment, can progress through stages that cause long-term and irreversible damage.

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Window and Incubation Period

The window period is how long after exposure you must wait before a test can reliably detect infection.

The incubation period is how long it takes for symptoms to appear.

For syphilis, the incubation period (time to symptoms) is usually around three weeks, while the window period (time until testing becomes accurate) is often 2 to 6 weeks. That means a person can test negative during the early window period even if they are already infected.

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Symptoms When They Occur

Many infections are silent or so mild that people do not recognize them.

Primary syphilis often appears as a single painless sore, known as a chancre, at the site of exposure.

Secondary syphilis may include a widespread rash, especially on the palms and soles, swollen lymph nodes, fever, patchy hair loss and mucous membrane lesions.

Latent syphilis has no symptoms, but the infection remains active inside the body.

Tertiary syphilis and neurosyphilis may develop years later and can affect the brain, heart, eyes, hearing, blood vessels, bones and joints. These later complications are irreversible, which is why early detection is critical.

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Complications if Untreated

Syphilis can cause serious long-term harm when untreated. This includes neurosyphilis with memory loss or stroke, cardiovascular syphilis with aortic aneurysms, ocular syphilis that damages vision, joint involvement, painful skin lesions, congenital syphilis in infants and increased risk of HIV transmission. All of these are preventable with appropriate diagnosis and treatment.

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Two Types of Tests and Why People Get Confused

Syphilis testing relies on two different categories of blood tests, and they work in very different ways — which is exactly why so many people (and many clinicians) get confused.

Nontreponemal Tests (RPR and VDRL)

These tests detect nonspecific antibodies that rise during active syphilis and fall after treatment. They produce a numerical titer, which clinicians use to determine disease activity and monitor treatment response.

But here’s where confusion sets in:

Nontreponemal tests can show a “positive” result for many reasons unrelated to syphilis. Because they respond to general inflammation and cell damage—not to the syphilis bacterium itself—false positives are surprisingly common. A reactive RPR/VDRL can be caused by:

• recent viral illnesses (including colds, flu, mono, COVID-19)
• autoimmune disease
• pregnancy
• older age
• certain vaccinations
• liver disease
• endocarditis
• malaria
• IV drug use
• or simply unexplained immune activation

These results are often low titer (like 1:1 or 1:2) and do not behave like true syphilis, which usually produces higher titers that change in predictable ways.

This is why a nontreponemal test cannot diagnose syphilis on its own. Without confirmation, false positives easily lead to panic, misdiagnosis, or unnecessary treatment.

Treponemal Tests (TP-PA, EIA, CIA)

Treponemal tests detect antibodies that are specific to Treponema pallidum, the syphilis bacterium. Once positive, these typically remain positive for life—even after successful treatment—which means they cannot distinguish between a new infection and one treated years ago.

Why the Algorithm Matters

CDC guidelines require both types of tests because each provides different, complementary information.

• If the treponemal test (screen) is positive, you must run a quantitative nontreponemal test to determine whether infection is active.
• If the results don’t match (for example, treponemal-positive but RPR-negative), a second treponemal test is needed to clarify whether this reflects a past treated infection, a false positive, or very early infection before RPR has risen.

Unfortunately, many providers misunderstand or skip parts of this algorithm, which leads to incorrect diagnoses and a lot of unnecessary fear.

Antibiotic Treatment and Resistance

Treatment depends on the stage of infection, but for most early syphilis cases the recommended therapy is intramuscular benzathine penicillin G. Unlike gonorrhea, syphilis has not developed widespread antibiotic resistance, making penicillin the cornerstone of treatment. More advanced forms such as neurosyphilis or ocular syphilis require specific regimens.

Modern prevention also includes DoxyPEP. While its strongest effect is against chlamydia and gonorrhea, research consistently shows that DoxyPEP reduces syphilis incidence in high-risk sexual networks. Shameless Care provides DoxyPEP for individuals who want proactive protection after sex.

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Reportable Infection Requirements

Syphilis is a reportable infection in all fifty states. When someone tests positive, both the laboratory and the diagnosing clinician must report the case to the patient’s local county health department. This includes identifying information such as name and address. Reporting enables partner services and public health intervention. Shameless Care follows these laws exactly and will never report anything beyond what is legally required.

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Reinfection and Partner Treatment

Reinfection is common, especially when partners are untreated or when someone enters a new sexual network. Because treponemal tests remain positive for life, monitoring relies on nontreponemal titers. Partner treatment and retesting on schedule are essential to prevent cycles of transmission.

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Pregnancy Considerations

Syphilis during pregnancy can cause miscarriage, stillbirth, preterm delivery and congenital infection that severely harms the newborn. Screening during pregnancy is mandatory in many areas, and treatment must be given immediately when infection is identified. Early detection dramatically reduces the risk of congenital disease.

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How Common Syphilis Really Is

After more than two decades of steady increases, recent data show encouraging signs of improvement. According to the CDC’s provisional 2024 surveillance report, primary and secondary syphilis declined by about twenty two percent from the previous year – likely due to DoxyPEP. This marks the second consecutive year of decline in the most infectious stages of syphilis.

Across all stages combined, syphilis also declined nationally in 2024, making this the second straight year of overall improvement rather than the third. This is a meaningful shift, though the long-term trend remains elevated compared with historical levels.

The most concerning trend is congenital syphilis. These cases continue to rise and reached nearly four thousand in the most recent reporting period. This indicates large gaps in prenatal screening, access to care and early treatment. Even as adult syphilis shows improvement, congenital syphilis remains a public health emergency.

Interpreting syphilis trends is complicated by testing algorithms. Treponemal tests alone cannot determine whether an infection is active, and nontreponemal titers require correct follow-up. Many providers still misuse testing algorithms, which can delay diagnosis or lead to misclassification.

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Contagiousness and Testing Timelines

People with untreated syphilis are infectious during primary and secondary stages and can still transmit infection during early latent stages. Sexual activity should be avoided until treatment is complete and all partners have been treated. Follow-up nontreponemal titers are recommended at defined intervals depending on the infection stage to ensure treatment success and detect reinfection.

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The Bottom Line

Syphilis is serious, systemic and improving only recently. It requires the correct combination of treponemal and nontreponemal testing, thoughtful interpretation and timely antibiotic treatment. A single syphilis test without proper follow-up does not tell the full story. If you are sexually active, comprehensive STI testing that includes syphilis serology is essential.

For complete protection you need a testing strategy that matches the realities of modern sexual health and a prevention strategy that stays ahead of risk.

Shameless Care offers the most complete at-home STI testing available, including treponemal-based syphilis screening interpreted by board-certified clinicians. We also offer DoxyPEP for those who want to significantly reduce the risk of syphilis, chlamydia and gonorrhea after sex.

If you want testing and prevention that align with how people actually have sex today, Shameless Care is here to help.