Why Syphilis Rates Are Rising: An Evergreen Explainer

What is syphilis and why does the rise matter

Syphilis is a bacterial sexually transmitted infection caused by Treponema pallidum. After decades of decline in many settings, syphilis rates have been rising since the mid‑2010s, with notable increases in congenital syphilis and among men who have sex with men. These trends matter because untreated syphilis can cause serious long term harm, and rising rates often signal broader gaps in prevention, testing, and care. This explainer outlines the main drivers, populations most affected, and what public health and clinical responses look like in an enduring context.

Key trends and demographic patterns

Increases in syphilis are not uniform. Many high income countries report rising rates among men who have sex with men, alongside persistent disparities among populations affected by social determinants of health. Congenital syphilis rates have also increased, reflecting missed opportunities for prenatal screening and treatment. The following table summarizes notable trends and their context.

Why syphilis rates are rising: main drivers

Multiple, interacting factors explain the upward trajectory. These include behavioral shifts, structural inequities, and changes in testing and case detection. Recognizing these drivers helps public health and clinicians target interventions more effectively.

• Condomless sex and partner mixing: Increased condomless sex and a larger, more interconnected pool of partners can facilitate spread within and between networks.
• Testing and diagnosis gaps: Reduced routine STI screening, especially outside traditional clinics, can delay diagnosis and increase onward transmission.
• Structural drivers: Poverty, unstable housing, criminalization of some populations, and limited access to care create conditions where syphilis can circulate more easily.
• Awareness and risk perception: Lower perceived risk and familiarity with syphilis symptoms can lead to delayed care-seeking and reduced partner notification.
• Congenial syphilis drivers: Lack of or delayed prenatal care, missed screening, and inadequate or untreated maternal infection contribute to congenital transmission.

Clinical presentation and complications of untreated syphilis

Understanding the stages and potential complications underscores why rising rates are a public health concern. Early detection and treatment remain highly effective at preventing progression.

Stages and key features

• Primary: Chancre at inoculation site, typically painless, with regional lymphadenopathy; chancre resolves even without treatment.
• Secondary: Mucocutaneous rash (often non itchy), generalized lymphadenopathy, mucosal lesions, and systemic symptoms such as fever and malaise.
• Latent: Serologic evidence of infection without clinical signs; early latent (first year) is often treated as potentially infectious, while late latent is generally less infectious but still consequential.
• Tertiary: Can involve cardiovascular syphilis, neurosyphilis, and gummatous disease, typically occurring years after infection if untreated.

Complications and special considerations

• Neurosyphilis can occur at any stage and may present with headache, cognitive changes, or motor deficits; it is diagnosed with cerebrospinal fluid evaluation in selected cases.
• Congenital syphilis can result in miscarriage, stillbirth, preterm birth, and severe neonatal morbidity if maternal infection is untreated or inadequately treated.
• Syphilis can increase both susceptibility to and transmissibility of HIV, making coinfection management and prevention especially important.

Testing approaches and algorithm considerations

Effective diagnosis relies on a structured approach that balances screening and confirmatory testing. Testing strategies should be guided by clinical presentation, local epidemiology, and individual risk factors.

• Nontreponemal tests: Quantitative assays such as RPR or VDRL are used for screening and to monitor treatment response; results can be reported as titers.
• Treponemal tests: EIAs, chemiluminescent assays, and TPPA are used to confirm exposure; most remain positive for life, so they do not reliably indicate active infection alone.
• Reverse sequence screening: In some settings, treponemal tests are used first, followed by nontreponemal testing for reactive samples; this can affect how algorithms are implemented locally.
• CSF testing: Indicated for neurosyphilis suspicion, HIV coinfection, or certain ocular presentations; clinical judgment and local guidelines should direct use.

Prevention, treatment, and public health strategies

Durably lower syphilis rates require a combination of individual level and population level actions. Clinicians and public health departments each have roles in reducing transmission and sequelae.

Clinical management points

• Penicillin remains the treatment of choice for all stages; regimens vary by stage and manifestations, including neurosyphilis.
• Doxycycline is an alternative for nonpregnant patients with penicillin allergy when appropriate, under clinical guidance.
• Expedited partner therapy and thorough sexual network notification can reduce reinfection and community spread.

Public health and systems approaches

• Routine, opt-out STI screening in clinical settings can improve case detection, especially in populations with limited access to care.
• Integrated services for people who inject drugs and linkage to care for people living with HIV reduce vulnerabilities that facilitate syphilis transmission.
• Community engagement, stigma reduction, and clear communication about risk and testing support sustained prevention efforts.
• For congenital syphilis, strong prenatal care pathways, timely maternal testing, and prompt treatment of pregnant people are essential.

Outlook and future directions

Persistent increases in syphilis underscore the need for adaptable, evidence informed strategies. Innovations in point of care testing, data linkage across labs and clinics, and targeted interventions in high risk networks can enhance response capacity. Ongoing evaluation of programs that integrate sexual health and social services will clarify which approaches best reduce transmission and inequities over time.