What are the modes of transmission of syphilis and how can it be prevented?

Syphilis Transmission and Prevention

Syphilis is transmitted primarily through direct contact with infectious mucocutaneous lesions during vaginal, anal, or oral sex, and vertically from mother to fetus during pregnancy, with prevention centered on routine screening, condom use, and doxycycline postexposure prophylaxis for high-risk populations. 1

Primary Modes of Transmission

Sexual Transmission

• Sexual contact with infectious lesions is the predominant route of transmission, occurring when mucocutaneous syphilitic lesions are present during vaginal, anal, or oral sex 1
• Transmission occurs only when active lesions are present, which are most common during primary and secondary stages 2
• Sexual transmission is uncommon after the first year of infection when active lesions typically resolve 2
• Transmission probability is highest during primary, secondary, and early-latent stages 2

Vertical (Mother-to-Child) Transmission

• Transplacental transmission from pregnant women to fetuses can occur at any stage of maternal infection 3
• Transmission rates approach 100% during primary and secondary syphilis in pregnancy 3
• Up to 40% of fetuses with in-utero syphilis exposure are stillborn or die during infancy 1
• Transmission risk decreases with increasing duration of maternal infection but remains significant 2
• Up to two-thirds of pregnant women with untreated syphilis develop adverse pregnancy outcomes including fetal loss, premature birth, congenital syphilis, and neonatal death 4

Other Transmission Routes

• Blood products and organ donation represent rare transmission routes 5
• Non-sexual direct contact with infectious lesions is theoretically possible but uncommon 5

High-Risk Populations

Adults at Increased Risk

• Men who have sex with men (MSM) comprised 32.7% of all males with primary and secondary syphilis in 2023 1
• People with HIV infection 1
• Individuals engaging in condomless sex with multiple partners 1
• Commercial sex workers 2
• Injection drug users 2
• Uninsured individuals and those living in poverty 2

Pregnant Women Requiring Enhanced Surveillance

• Women in areas with high syphilis prevalence 2
• Women with inadequate prenatal care access 3
• Women in emergency departments, jails, and prisons 2

Prevention Strategies

Screening Recommendations

For General Population:

• Screen all sexually active people aged 15-44 years at least once 1
• Screen at least annually for those at increased risk 1
• Routine screening of MSM can identify infections before progression to symptomatic disease 6

For Pregnant Women:

• Screen 3 times during pregnancy: at first prenatal visit, during third trimester (28-32 weeks), and at delivery 1, 2
• In high-prevalence areas or high-risk women, repeat testing at 28-32 weeks of gestation and delivery is essential 2
• All women delivering stillborn infants after 20 weeks gestation must be tested 2
• No infant should leave the hospital without documentation of maternal syphilis serology status 2

Behavioral Prevention

Condom Use:

• Counseling about consistent condom use reduces transmission risk 1, 5
• Condoms provide barrier protection against contact with infectious lesions 5

Postexposure Prophylaxis:

• Offer doxycycline postexposure prophylaxis (200 mg taken within 72 hours after sex) to MSM and transgender women with a history of sexually transmitted infection in the past year 1
• This represents a new evidence-based prevention strategy for high-risk populations 1

Partner Management

• Sexual partners exposed within 90 days to someone with primary, secondary, or early latent syphilis should receive presumptive treatment even if seronegative 2
• Partners exposed more than 90 days before should be treated presumptively if serologic results are unavailable and follow-up uncertain 2
• Long-term partners of patients with late syphilis require clinical and serologic evaluation 2

Critical Prevention Considerations

Timing of Maternal Treatment

• Detection and treatment before 28 weeks gestation can reduce adverse pregnancy outcomes to background rates 4
• Treatment after 28 weeks still provides benefit but with higher risk of adverse outcomes 4
• Syphilis interventions during pregnancy demonstrate an 80% reduction in stillbirths, superior to interventions for malaria (22%), HIV (7%), or bacterial vaginosis (12%) 4

Common Pitfalls

• Failure to rescreen pregnant women in the third trimester misses 46.8% of cases acquired after initial nonreactive testing 3
• Delayed prenatal care access contributed to 30.9% of congenital syphilis cases 3
• Partner notification effectiveness has decreased because many partners are anonymous, particularly among MSM 6
• Azithromycin is not recommended for prevention due to treatment failures and macrolide-resistant T. pallidum 2

Systems-Level Failures

• The 937% increase in congenital syphilis cases over the past decade reflects dismantling of public health infrastructure 7
• American Indian/Alaska Native communities face rates up to 100 times higher than White populations in some regions 7
• Cyclical boom-and-bust funding, workforce deterioration, and fragmented surveillance systems contribute to prevention failures 7