Clinical Development and Performance of the First To Know Syphilis Self-Test for Over-the-Counter Usage: a De Novo Rapid Test for Treponemal Antibody

ABSTRACT The resurgence of syphilis in the USA and globally has hastened the need for widely available syphilis testing. Early detection of syphilis is crucial for avoiding serious clinical complications and preventing spread of infection. Self-tests enhance access to testing and promote timely treatment for positive cases. Herein we describe the performance of First to Know Syphilis Test (FTK), the first over the counter (OTC) treponemal test. A prospective multi-site clinical study with 1270 subjects was conducted, where subjects self-collected fingerstick capillary blood and self-tested without assistance. FTK test results were compared with a composite reference standard to evaluate diagnostic performance. The FTK test exhibited an overall sensitivity of 93.4% (95% CI, 87.0% to 96.8%) and specificity of 99.5% (95% CI, 98.9% - 99.8%) and accuracy of 99%. The overall agreement was 98.9%, with Cohens Kappa (ⱪ) value 0.93 (95% CI, 0.90 to 0.97) showing excellent agreement between the reference standard and FTK results. In addition, the test was validated in a panel of 125 clinically staged syphilis patient samples and the results showed 100% agreement in detecting anti-treponemal antibodies in all the samples. These data show excellent performance of the FTK Test demonstrating its utility in the screening and diagnosis of syphilis. The availability of this OTC test and its excellent performance at low prevalence, will have a profound impact on syphilis detection and prevention strategies and could reduce co morbidities such as HIV and other STI transmission. Competing Interest Statement Competing Interest Statement All authors are employees of Now Diagnostics. AGJ is a scientific consultant of Now Diagnostics. LN is marketing consultant and RP is project management consultant for Now Diagnostics. All other authors have disclosed that they have no conflicts of interest Funding Statement This study was funded internally by NOW Diagnostics. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics Statement This study was conducted in accordance with the ethical standards of the Helsinki Declaration. IRB approval for the multi-site study was obtained from Advarra IRB #Pro00032035. 13 The initial approval was on Dec 9, 2019, and latest approval was on July 25, 2023. Informed consent was obtained from all study subjects, and all the participant data were de-identified in the database. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Footnotes with a correction in the text and supplemental figure as below: -Abstract ; "three reference standards.." changed to " composite reference standard -Supplemental figure 1A noted NPV instead of PPV (like that was found in the first version in Medrxiv) This is corrected Data Availability Statement All data supporting the findings of this research study are described in the manuscript and relevant details are available upon reasonable request. Due to the involvement of human subjects and nature of the STI study, the datasets are not shared in public repositories due to the limitations on ethical and privacy concerns.