Can Syphilis Spread?
Yes, syphilis is highly transmissible through direct contact with infectious lesions during sexual activity, and can also spread from mother to fetus during pregnancy, causing congenital syphilis. 1, 2
Primary Routes of Transmission
Sexual Transmission
Sexual transmission of T. pallidum occurs only when mucocutaneous syphilitic lesions are present, which are most common during the first year of infection 1, 2. The bacteria spreads through:
- Vaginal, anal, or oral sex with contact to infectious lesions 3
- Direct contact with primary chancres (painless anogenital ulcers)
- Contact with secondary syphilis lesions including diffuse rashes and mucocutaneous lesions
- Female-to-female transmission through oral-genital contact has been documented 4
Critical timing for infectiousness: Lesions are uncommon after the first year of infection, making late-stage syphilis much less transmissible sexually 1, 2.
Vertical (Mother-to-Fetus) Transmission
Syphilis crosses the placenta during pregnancy, with devastating consequences 2, 5:
- Up to 40% of fetuses with in-utero exposure are stillborn or die during infancy 3
- Transmission can occur at any stage of maternal infection
- Congenital syphilis cases increased 106% from 2019-2023 in the US 3
- American Indian/Alaska Native communities face rates up to 100 times higher than White populations 6
Non-Sexual Transmission (Rare but Important)
While uncommon, non-sexual transmission can occur through:
- Direct contact with active lesions in overcrowded households with poor hygiene 7
- Mouth-to-mouth transfer of pre-chewed food from infected caregivers to infants 8
- Kissing, breast-feeding, or handling by actively infected individuals 8
- These routes are particularly relevant in children presenting with atypical rashes when family members have active syphilis 7, 8
Partner Management and Exposure Risk
All sexual partners require evaluation and often presumptive treatment based on timing of exposure 1, 2:
High-Risk Exposures Requiring Presumptive Treatment:
- Exposure within 90 days of partner's diagnosis of primary, secondary, or early latent syphilis—treat presumptively even if seronegative 2
- Exposure >90 days before diagnosis—treat presumptively if serologic results unavailable and follow-up uncertain 2
Time Periods for Partner Notification:
- Primary syphilis: 3 months plus duration of symptoms
- Secondary syphilis: 6 months plus duration of symptoms
- Early latent syphilis: 1 year 1, 2
Current Epidemiologic Context
The transmission risk must be understood in the context of the current epidemic 3, 9:
- US syphilis cases increased 61% from 2019-2023
- Diagnoses among females increased 112% in the same period
- Men who have sex with men (MSM) comprised 32.7% of all males with primary and secondary syphilis in 2023
- Rates among women nearly tripled from 2015-2019
Critical Clinical Pitfall
Do not assume late-stage or latent syphilis is non-infectious. While sexual transmission is uncommon after the first year, long-term sex partners of patients with late syphilis should still be evaluated clinically and serologically 1, 2. Additionally, pregnant women with any stage of syphilis can transmit to the fetus, making maternal screening at first prenatal visit, 28-32 weeks, and delivery essential 5, 2.