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NCT Number: NCT07300254

Treponemal Shedding, Load, and Viability, in Women and Men-who-have-sex-with-women-only With Early Infectious Syphilis: Implications for Transmission

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.

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Key information

Conditions

Syphilis Bacterial Infections Bacterial Infections and Mycoses Communicable Diseases Genital Diseases Gram-Negative Bacterial Infections Infections Sexually Transmitted Diseases Sexually Transmitted Diseases, Bacterial Spirochaetales Infections Treponemal Infections Urogenital Diseases

Age range

18 year and older

Sex eligibility

All sexes

Study type

Observational

Primary location

Monash University, Melbourne, Victoria, Australia

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Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • 1. Any cis-woman, cis-MSW, or nonbinary individuals with a penis who have sex with women only, (who meet all other study criteria) 2. Aged ≥18 years of age, 3. At least one sexual partner in the last 12 months 4. One of either:

a. Untreated clinically suspected primary or secondary syphilis. i. Must have rash or lesion(s) clinically suggestive of early infectious syphilis infection.

ii. May have positive PCR result, positive Dark-ground Microscopy result, positive syphilis serology or positive point-of-care syphilis test, but these are not necessary at the time of enrolment.

b. Untreated early latent (no clinical signs indicative of primary or secondary syphilis) syphilis with positive syphilis serology or positive point-of-care test, and one or more of the following(11): i. A documented syphilis seroconversion within the prior 12 months. ii. A sustained (longer than 2 weeks) fourfold or greater increase in the titre in the prior 12 months in a person previously treated for syphilis.

iii. Unequivocal symptoms of primary or secondary syphilis within the prior 12 months.

iv. Contact in the prior 12 months with a sex partner who had untreated primary, secondary, or early latent syphilis.

v. Documented reactive nontreponemal and treponemal tests, and the only possible exposure occurred during the previous 12 months vi. RPR/VDRL titre >= 1:64 5. Be willing and able to complete study procedures, including physical examination 6. Receiving syphilis treatment on the day of recruitment 7. Have sufficient language proficiency to understand the requirements of the study 8. Provide informed consent as per individual site's local ethics requirements

Exclusion criteria

  • Men, transwomen, or other people, with a penis, who have had any sexual contact, including kissing, oral sex or anal sex, with men (or any other individual with a penis) in the previous one year.
  • Individuals who have received antibiotic treatment within 1 month prior to enrolment, with the EXCEPTION of metronidazole.
  • Diagnosis of late latent syphilis (>1 year) or latent syphilis of unknown duration.

Treatment and study plan

No Intervention: Observational Cohort

Other

No intervention: Observational study

Primary outcomes

  1. Number of Biological Samples Testing Positive for Treponema pallidum DNA by PCR

    Time frame: Samples are taken at time of consent - single visit study

    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).

Secondary outcomes

  1. Load of Treponema pallidum DNA in Positive Biological Samples by In-house Quantitative PCR (qPCR) assay

    Time frame: Samples are taken at time of consent - single visit study

    This outcome measures the load (copies/mL) of Treponema pallidum (Tp) DNA in collected biological samples-including lesion swabs, blood, urine, saliva, and oral/anal/genital swabs-using an in-house validated quantitative T. pallidum polymerase chain reaction (Tp qPCR) assay.

    Data will be reported as a comparison in load between anatomical sites and by clinical stage of syphilis.

  2. Number of Treponema pallidum-Positive Samples Demonstrating Viable Organisms via Novel In-house Viability Assay

    Time frame: Samples are collected at time of consent - single study visit

    This outcome measures the viability of detected Treponema pallidum in PCR-positive biological samples. Viability is assessed using a novel in-house viability assay.

    Results will be summarised as the number and proportion of Tp PCR-positive samples that contain viable organisms, stratified by sample type and clinical/epidemiological variables specified in the SOS Global protocol.

    This outcome focuses on confirming whether Tp organisms in collected specimens are capable of establishing infection, rather than merely detecting genetic material. The viability assessment does not result in a continuous scale; it is a binary laboratory outcome (viable / non-viable).

Study contacts

Contact information is provided by the study sponsor or research team.

Brigid M Scally

CONTACT

[email protected]

+61399039300

Janet Towns

CONTACT

[email protected]

Sponsors and collaborators

Lead sponsor

Monash University

Other

Collaborators

  • Melbourne Sexual Health Centre
  • The Alfred

Registry information

Official study title

Treponemal Shedding, Load, and Viability, in Women and Men-who-have-sex-with-women Only With Early Infectious Syphilis: Implications for Transmission

Acronym: SOS Global

Important dates

Study start
2025
Primary completion
2027
Study completion
2028
First posted
Dec 23, 2025
Registry last updated
Apr 3, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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