Brief Summary

How syphilis is transmitted between sexual partners is unclear. Asymptomatic detection i.e. detection of syphilis bacteria (Tp) from anatomical sites without lesions, in patients with syphilis infection, suggests that asymptomatic transmission from these sites may play a role. However, no existing studies have established whether the syphilis bacteria (Tp) detected was viable. This means it is not known if the bacteria at this anatomical site is alive and therefore able to transmit the infection. Further, studies have focused mostly on men who have sex with men, resulting in a lack of evidence regarding anal shedding in men-who-have-sex-with-women only and women (regardless of sexual behaviour), and no data on asymptomatic vaginal shedding in women. This study will explore:

1.Patterns of Tp detection in women and men-who-have-sex-with-women only.
2.Whether detected Tp from each asymptomatic anatomical sites is viable
3.Duration of Tp detection and viability (alive and transmissible bacteria). Patients presenting to a participating sexual health service (overseas only) for management of suspected/confirmed early infectious syphilis will be eligible. During the routine clinical examination, participants will have additional oral and anal swabs, urine, vaginal swab (where relevant), penile skin swab (where relevant) and blood sample collected, in addition to the routine samples taken from the same sites and routine serology collected when syphilis is diagnosed.

Trial Health

On Track

Trial Health Score

Automated assessment based on enrollment pace, timeline, and geographic reach

Enrollment

480

participants targeted

Target at P75+ for all trials

Timeline

33mo left

Started Dec 2025

Typical duration for all trials

Geographic Reach

4 countries

8 active sites

Status

recruiting

Health score is calculated from publicly available data and should be used for screening purposes only.

Trial Relationships

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Study Timeline

Key milestones and dates

3.1 years study duration

Study Progress14%

Dec 2025Dec 2028

Study Start

First participant enrolled

December 2, 2025

Completed

8 days until next milestone

First Submitted

Initial submission to the registry

December 10, 2025

Completed

13 days until next milestone

First Posted

Study publicly available on registry

December 23, 2025

Completed

1.5 years until next milestone

Primary Completion

Last participant's last visit for primary outcome

June 30, 2027

Expected

1.5 years until next milestone

Study Completion

Last participant's last visit for all outcomes

December 31, 2028

Last Updated

January 22, 2026

Status Verified

January 1, 2026

Enrollment Period

1.6 years

First QC Date

December 10, 2025

Last Update Submit

January 20, 2026

Conditions

Syphilis

Keywords

syphilissexual healthsyphilis transmissionasymptomatic shedding

Outcome Measures

Primary Outcomes (1)

Number of Biological Samples Testing Positive for Treponema pallidum DNA by PCR
This outcome measures the presence of Treponema pallidum (Tp) DNA in collected biological samples-including lesion swabs, blood, urine, saliva, and oral/anal/genital swabs-using a validated T. pallidum polymerase chain reaction (Tp PCR) assay. Data will be reported as the number and proportion of samples that test positive, stratified by: * sample type, * clinical stage of syphilis, * anatomical site (where applicable), * and participant characteristics relevant to the SOS Global protocol. No scale is used; this is a binary laboratory outcome (PCR positive / PCR negative).
Samples are taken at time of consent - single visit study