We reviewed relevant syphilis diagnostic literature to address the question “What diagnostic considerations should be taken into account when screening for syphilis using the traditional or reverse algorithm?” Improved laboratory diagnosis of syphilis is an important element of the effort to reduce syphilis rates. Screening for syphilis is performed using either a nontreponemal or treponemal test (part of the traditional or reverse algorithm, respectively). Both syphilis algorithms are used by laboratories. However, there are limited data on the performance and cost-effectiveness of the algorithms. An expert panel generated “key questions” in the laboratory diagnosis of syphilis. This paper pertains to the key factors that should be considered when deciding whether to screen for syphilis using either the traditional or the reverse algorithm. A systematic literature review was performed, and tables of evidence were created to address this question.

The idea of specimen self-collection or self-STI testing is not new. In 2019, the World Health Organization (WHO) published the “WHO Consolidated Guideline on Self-Care Interventions for Health” as a first installment in a planned series for various diseases (8). The first document focused on “Sexual and Reproductive Health and Rights”. Self-care including self-testing has the readily apparent benefits of privacy, confidentiality, speed, convenience, and access if the price is affordable. It is “people-centered” (9) and enables active participation in one’s own health. It is also a health system approach as it can reduce burden on stretched systems with world-wide shortages in medical personnel or other barriers to health care access. Potential risks include: low specimen return rates, uncertain follow-up (linkage to care including treatment, repeat testing including test of cure, partner notification, counseling on risk reduction), unintended/unnecessary use (resulting in false positives with their own set of associated problems), incorrect use, lack of understanding of window periods (resulting in false negatives), lack of surveillance data generation, among other issues (9). The WHO systematically reviewed evidence for self-testing or specimen self-collection for GC, CT and syphilis, including US studies, and published a meta-analysis of available evidence (9). Programs offering self-collection of samples increased overall uptake of STI testing services (RR: 2.941, 95% CI 1.188 to 7.281) and case finding (RR: 2.166, 95% CI1.043 to 4.498), prior to the pandemic (9). U. S. laboratory research on the equivalence and/or superiority of self-collected versus provider-collected specimens for test sensitivity was reported by Gaydos et al (summarized or referenced in (10)). Based on this evidence, WHO issued a new recommendation in 2019 “Self-collection of samples for Neisseria gonorrhoeae and Chlamydia trachomatis should be made available as an additional approach to deliver STI testing services for individuals using STI testing services” (8). In addition, WHO issued a new and conditional recommendation: “Self-collection of samples for Treponema pallidum (syphilis) and Trichomonas vaginalis may be considered as an additional approach to deliver STI testing services for Individuals using STI testing services” (8). Thus, even before the COVID-19 pandemic, substantial expert agreement existed concerning benefits of this approach.

Serological diagnosis of syphilis depends on assays that detect treponemal and nontreponemal antibodies. Laboratory certification and trained personnel are needed to perform most of these tests, while high costs and long turnaround time can hinder treatment initiation or linkage to care. A rapid treponemal syphilis test (RST) that is simple to perform, accessible, and inexpensive would be ideal. The Syphilis Health Check (SHC) assay is the only Food and Drug Administration (FDA)-cleared and Clinical Laboratory Improvement Amendments (CLIA)-waived RST in the United States. In this study, 1,406 archived human serum samples were tested using SHC and traditional treponemal and nontreponemal assays. Rapid test results were compared with treponemal data alone and with a laboratory test panel consensus defined as being reactive by both treponemal and nontreponemal assays for a given specimen, or nonreactive by both types of assays. The sensitivity and specificity of the SHC assay compared with treponemal tests alone were 88.7% (95% confidence interval [CI], 86.2 to 90.0%) and 93.1% (95% CI, 90.0 to 94.9%), respectively, while comparison with the laboratory test panel consensus showed 95.7% (95% CI, 93.6 to 97.2%) sensitivity and 93.2% (95% CI, 91.0 to 95.1%) specificity. The data were further stratified based on age, sex, pregnancy, and HIV status. The sensitivity and specificity of the SHC assay ranged from 66.7% (95% CI, 46.0 to 83.5%) to 91.7% (95% CI, 87.7 to 94.7%) and 88% (95% CI, 68.8 to 97.5%) to 100% (95% CI, 47.8 to 100%), respectively, across groups compared to traditional treponemal assays, generally increasing for all groups except the HIV-positive (HIV) population when factoring in the laboratory test panel consensus. These data contribute to current knowledge of the SHC assay performance for distinct populations and may guide use in various settings.

The Centers for Disease Control and Prevention’s (CDC) Division of STD Prevention, in collaboration with the Association of Public Health Laboratories (APHL), is developing a nationally available syphilis serum repository for research of Food and Drug Administration (FDA)-cleared or investigational syphilis diagnostic assays in the United States. State and local public health laboratories (PHL) submitted de-identified residual sera with information on collection date, volume, storage conditions, freeze-thaw cycles, PHL serology results, reported syphilis stage and demographic details if available. Previous test results were blinded and sera (N=152 reported syphilis stage, N = 131 unknown status) were tested at CDC using five FDA-cleared and one investigational syphilis tests. Treponemal and nontreponemal test sensitivity ranged from 76.3–100% and 63.2–100%, respectively, among staged specimens. The conventional treponemal assays showed high concordance of 95.4%. By providing syphilis stage and comprehensive serological test data, developed repository may serve as a valuable resource for diagnostic test validation studies.