Syphilis Transmission
Syphilis is transmitted primarily through direct contact with mucocutaneous syphilitic lesions during sexual activity, and transmission occurs only when these infectious lesions are present, which is uncommon after the first year of infection. 1
Primary Modes of Transmission
Sexual Transmission
- Direct contact with infectious lesions is the primary route of syphilis transmission, occurring through vaginal, anal, or oral sexual contact 1, 2
- Transmission is limited to early stages: Sexual transmission of T. pallidum occurs only when mucocutaneous syphilitic lesions are present, and such manifestations are uncommon after the first year of infection 1
- Oral transmission is documented: Oral swab samples can be positive for T. pallidum even in the absence of visible oral lesions, highlighting the importance of serologic screening regardless of symptoms 1
- Female-to-female transmission can occur through oral-genital sexual contact 3
Vertical (Maternal-Fetal) Transmission
- Congenital syphilis results from transplacental transmission during pregnancy, representing a major public health concern with cases increasing 937% over the past decade 4, 5
- Transmission occurs at any stage of maternal infection, though the risk is highest with untreated early syphilis 6, 4
- Transmission during delivery through contact with infectious lesions in the birth canal can also occur 7
Blood Products and Organ Donation
- Transmission via blood transfusion is possible but rare in modern blood banking systems 2, 6
- Organ donation represents a potential transmission route 2
Non-Sexual Contact
- Direct contact with infectious lesions through non-sexual means is theoretically possible but extremely rare 6
- Transmission through infected milk or breasts was historically considered but is not a significant modern transmission route 7
Critical Timing Considerations for Infectiousness
The infectious period varies by stage of syphilis and is crucial for partner management:
- Primary syphilis: 3 months plus duration of symptoms 1
- Secondary syphilis: 6 months plus duration of symptoms 1
- Early latent syphilis: 1 year 1
- Late latent and tertiary syphilis: Rarely contagious 4
Partner Management Based on Transmission Risk
Persons exposed within 90 days preceding the diagnosis of primary, secondary, or early latent syphilis in a sex partner might be infected even if seronegative and should be treated presumptively 1
Persons exposed >90 days before diagnosis should be treated presumptively if serologic test results are not available immediately and follow-up is uncertain 1
Clinical Pitfalls
Atypical presentations complicate transmission assessment: Primary syphilitic chancres may be multiple and painful, contradicting the traditional teaching of a single painless lesion 1. This atypical presentation may lead to missed diagnoses and continued transmission.
Asymptomatic oral carriage: Patients may have positive oral swabs for T. pallidum without visible oral lesions, though the infectiousness of these cases remains unclear 1