Clinical Test Performance of a Rapid Point-of-Care Syphilis Treponemal Antibody Test: A Systematic Review and Meta-analysis

A novel syphilis Treponema pallidum lipoprotein peptide antigen diagnostic assay using red cell kodecytes in routine blood centre column agglutination testing platforms

BACKGROUND AND OBJECTIVES

The detection of treponemal antibodies, which are used to make a diagnosis of syphilis, is important both for diagnostic purposes and as a mandatory blood donor test in most countries. We evaluated the feasibility of using Kode Technology to make syphilis peptide red cell kodecytes for use in column agglutination serologic platforms.

MATERIALS AND METHODS

Candidate Kode Technology function-spacer-lipid (FSL) constructs were made for the Treponema pallidum lipoprotein (TmpA) of T. pallidum, using the peptide and FSL selection algorithms, and then used to make kodecytes. Developmental kodecytes were evaluated against a large range of syphilis antibody reactive and non-reactive samples in column agglutination platforms and compared against established methodologies. Overall, 150 reactive and 2072 non-reactive Syphicheck assay (a modified T. pallidum particle agglutination) blood donor samples were used to evaluate the agreement rate of the developed kodecyte assay.

RESULTS

From three FSL-peptide candidate constructs, one was found to be the most suitable for diagnostics. Of 150 Syphicheck assay reactive samples, 146 were TmpA-kodecyte reactive (97.3% agreement), compared with 58.0% with the rapid plasmin reagin (RPR) assay for the same samples. Against the 2072 expected syphilis non-reactive samples the agreement rate for TmpA-kodecytes was 98.8%.

CONCLUSION

TmpA-kodecytes are viable for use as cost-effective serologic reagent red cells for the detection of treponemal antibodies to diagnose syphilis with a high level of specificity in blood centres. This kodecyte methodology also potentially allows for introduction of the reverse-algorithm testing into low-volume laboratories, by utilizing existing transfusion laboratory infrastructure.

Clinical Updates in Sexually Transmitted Infections, 2024

Sexually transmitted infections (STIs) continue to increase in the United States with more than 2.5 million cases of gonorrhea, chlamydia, and syphilis reported to the Centers for Disease Control and Prevention in 2022. Untreated STIs in women can lead to adverse outcomes, including pelvic inflammatory disease, infertility, chronic pelvic pain, and pregnancy complications such as ectopic pregnancy, early pregnancy loss, stillbirth, and neonatal transmission. STI-related guidelines can be complex and are frequently updated, making it challenging to stay informed on current guidance. This article provides high-yield updates to support clinicians managing STIs by highlighting changes in screening, diagnosis, and treatment. One important topic includes new guidance on syphilis screening, including a clarified description of high community rates of syphilis based on Healthy People 2030 goals, defined as a case rate of primary or secondary syphilis > 4.6 per 100,000. Reproductive aged persons living in counties above this threshold should be offered syphilis screening. Additionally, American College of Obstetricians & Gynecologists now recommends syphilis screening three times during pregnancy regardless of risk-at the first prenatal visit, during the third trimester, and at delivery. In addition, new guidance to support consideration for extragenital screening for gonorrhea and chlamydia in women at sites such as the anus and pharynx is discussed. Other topics include the most recent chlamydia, gonorrhea, trichomoniasis, and pelvic inflammatory disease treatment recommendations; screening and treatment guidance for Mycoplasma genitalium; genital herpes screening indications and current diagnostic challenges; and the diagnosis and management of mpox in women and during pregnancy.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

CDC Laboratory Recommendations for Syphilis Testing, United States, 2024

This report provides new CDC recommendations for tests that can support a diagnosis of syphilis, including serologic testing and methods for the identification of the causative agent Treponema pallidum. These comprehensive recommendations are the first published by CDC on laboratory testing for syphilis, which has traditionally been based on serologic algorithms to detect a humoral immune response to T. pallidum. These tests can be divided into nontreponemal and treponemal tests depending on whether they detect antibodies that are broadly reactive to lipoidal antigens shared by both host and T. pallidum or antibodies specific to T. pallidum, respectively. Both types of tests must be used in conjunction to help distinguish between an untreated infection or a past infection that has been successfully treated. Newer serologic tests allow for laboratory automation but must be used in an algorithm, which also can involve older manual serologic tests. Direct detection of T. pallidum continues to evolve from microscopic examination of material from lesions for visualization of T. pallidum to molecular detection of the organism. Limited point-of-care tests for syphilis are available in the United States; increased availability of point-of-care tests that are sensitive and specific could facilitate expansion of screening programs and reduce the time from test result to treatment. These recommendations are intended for use by clinical laboratory directors, laboratory staff, clinicians, and disease control personnel who must choose among the multiple available testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients. Future revisions to these recommendations will be based on new research or technologic advancements for syphilis clinical laboratory science.

Sensitivity and specificity of a syphilis rapid diagnostic test in blood donors' samples

Rapid Diagnostic Tests (RDT) are useful to identify syphilis cases, particularly for hard-to-reach populations and if laboratory services are scarce. However, RDT performance may be suboptimal. We aimed to assess the sensitivity and specificity of a syphilis RDT using well-characterized blood donors' samples. We categorized samples from 811 blood donors into five groups: 1 - Samples with reactive Chemiluminescence (QML), FTA-Abs, and VDRL; 2 - Samples with reactive QML and FTA-Abs, and nonreactive VDRL; 3 - Samples with reactive QML, and nonreactive for other markers (false-positives); 4 - Controls with nonreactive QML; and 5 - Samples reactive for HIV, with nonreactive QML. Sensitivity was tested in groups 1 (overall and according to VDRL titers) and 2; specificity was tested in groups 3‒5. The RDT had high specificity, even in samples reactive for HIV. The sensitivity was high (91.9%) in samples with reactive VDRL but varied between 75.0%‒100% according to VDRL titers. The overall sensitivity was lower (81.3%) in samples with reactive FTA-Abs and nonreactive VDRL. The RDT is a useful tool to detect active syphilis but may be more limited for cases with very early or remote infection, or those with prior treatment. When higher sensitivity is needed, additional strategies including recurrent testing or laboratory-based tests may be required.

Computational methods applied to syphilis: where are we, and where are we going?

Syphilis is an infectious disease that can be diagnosed and treated cheaply. Despite being a curable condition, the syphilis rate is increasing worldwide. In this sense, computational methods can analyze data and assist managers in formulating new public policies for preventing and controlling sexually transmitted infections (STIs). Computational techniques can integrate knowledge from experiences and, through an inference mechanism, apply conditions to a database that seeks to explain data behavior. This systematic review analyzed studies that use computational methods to establish or improve syphilis-related aspects. Our review shows the usefulness of computational tools to promote the overall understanding of syphilis, a global problem, to guide public policy and practice, to target better public health interventions such as surveillance and prevention, health service delivery, and the optimal use of diagnostic tools. The review was conducted according to PRISMA 2020 Statement and used several quality criteria to include studies. The publications chosen to compose this review were gathered from Science Direct, Web of Science, Springer, Scopus, ACM Digital Library, and PubMed databases. Then, studies published between 2015 and 2022 were selected. The review identified 1,991 studies. After applying inclusion, exclusion, and study quality assessment criteria, 26 primary studies were included in the final analysis. The results show different computational approaches, including countless Machine Learning algorithmic models, and three sub-areas of application in the context of syphilis: surveillance (61.54%), diagnosis (34.62%), and health policy evaluation (3.85%). These computational approaches are promising and capable of being tools to support syphilis control and surveillance actions.

Syphilis

Syphilis is an important public health problem in the U.S. and many high-income nations. The rates of syphilis continue to increase and there is an urgent need for medical providers of a variety of backgrounds to recognize this disease. In this review, we cover the key clinical findings of syphilis and provide an overview of the diagnosis and management of this disease in adults.

Lifetime prevalence of syphilis infection among predominantly Black sexual and gender minorities living with HIV in Atlanta, Georgia: a cross-sectional analysis

OBJECTIVES

Syphilis infection disproportionately impacts Black sexual and gender minorities (SGM) in the United States. The extent of this impact among those living with HIV has been minimally examined. This study sought to examine lifetime syphilis prevalence and associated factors in a community sample of predominantly Black SGM living with HIV in the Southeastern US.

DESIGN

Participants (N = 174) enrolled in a stigma-mitigation trial for people living with HIV in Atlanta, Georgia, completed a sub-study involving testing for Treponema pallidum antibodies, indicative of lifetime syphilis infection. We performed chi-square and Fisher's exact tests to assess sociodemographic and healthcare differences by presence/absence of lifetime syphilis infection.

RESULTS

Most participants identified as non-Hispanic Black (n = 142/174; 81.6%) and cisgender male (n = 146/174; 83.9%). More than two thirds (n = 120/174) identified as gay/homosexual. We documented a 55.7% (n = 97/174) lifetime prevalence of syphilis infection and observed differences by sexual identity, with 77.3% (n = 75/97) of those screening positive reporting gay/homosexual identity relative to 58.4% (n = 45/77) of those screening negative (chi-square[1] = 7.8, p < 0.010).

CONCLUSION

Findings underscore how syphilis prevention efforts have missed the most marginalized, warranting a renewed, comprehensive strategy for improving the sexual health of Black SGM. Embedding targeted, respectful community engagement, expanded testing access, and healthcare provider training into broader sexual health and psychosocial wellness efforts is needed.

Screening for Syphilis Infection in Nonpregnant Adolescents and Adults: US Preventive Services Task Force Reaffirmation Recommendation Statement

IMPORTANCE

Syphilis is a sexually transmitted infection that can progress through different stages (primary, secondary, latent, and tertiary) and cause serious health problems if left untreated. Reported cases of primary and secondary syphilis in the US increased from a record low of 2.1 cases per 100 000 population in 2000 and 2001 to 11.9 cases per 100 000 population in 2019. Men account for the majority of cases (83% of primary and secondary syphilis cases in 2019), and rates among women nearly tripled from 2015 to 2019.

OBJECTIVE

To reaffirm its 2016 recommendation, the US Preventive Services Task Force (USPSTF) commissioned a reaffirmation evidence update focusing on targeted key questions evaluating the performance of risk assessment tools and the benefits and harms of screening for syphilis in nonpregnant adolescents and adults.

POPULATION

Asymptomatic, nonpregnant adolescents and adults who have ever been sexually active and are at increased risk for syphilis infection.

EVIDENCE ASSESSMENT

Using a reaffirmation process, the USPSTF concludes with high certainty that there is a substantial net benefit of screening for syphilis infection in nonpregnant persons who are at increased risk for infection.

RECOMMENDATION

The USPSTF recommends screening for syphilis infection in persons who are at increased risk for infection. (A recommendation).

Point-of-Care Diagnostics for Diagnosis of Active Syphilis Infection: Needs, Challenges and the Way Forward

Syphilis, a curable sexually transmitted infection, has re-emerged as a global public health threat with an estimated 5.6 million new cases every year. Pregnant women and men who have sex with men are key target populations for syphilis control and prevention programs. Frequent syphilis testing for timely and accurate diagnosis of active infections for appropriate clinical management is a key strategy to effectively prevent disease transmission. However, there are persistent challenges in the diagnostic landscape and service delivery/testing models that hinder global syphilis control efforts. In this commentary, we summarise the current trends and challenges in diagnosis of active syphilis infection and identify the data gaps and key areas for research and development of novel point-of-care diagnostics which could help to overcome the present technological, individual and structural barriers in access to syphilis testing. We present expert opinion on future research which will be required to accelerate the validation and implementation of new point-of-care diagnostics in real-world settings.

Laboratory Evaluation of the DPP Syphilis Screen & Confirm Assay

Because syphilis is a public health concern, new strategies and tools for detecting active syphilis cases should be evaluated for future implementation. We assessed the laboratory performance of the DPP Syphilis Screen & Confirm rapid immunodiagnostic test (Chembio Diagnostics, Medford, NY, USA), using visual reading and the manufacturer's electronic test microreader, for detection of treponemal and nontreponemal antibodies in 383 fully characterized stored serum specimens. We used the Treponema pallidum particle agglutination (TPPA) test and rapid plasma reagin (RPR) test as reference tests for the DPP Syphilis Screen & Confirm assay treponemal and nontreponemal components, respectively. The sensitivity values for treponemal antibody detection by electronic reader and visual interpretation were 83.2% and 85.9%, respectively, with 100% specificity. For nontreponemal antibody detection, the sensitivity values were 65.7% and 69.0% and the specificity values were 88.7% and 89.4% for electronic reader and visual interpretation, respectively. There was excellent correlation between visual interpretation and the microreader for either component (kappa coefficient, 0.953). When restricting the analysis to RPR titers of ≥1:8, the sensitivity was 96.9% for either reading method; numerical microreader values showed good correlation with RPR titers (Spearman rho of 0.77). The DPP Syphilis Screen & Confirm assay showed good performance, compared to reference syphilis tests, using serum. Field evaluation studies should be done to validate its use for detection of active cases and for monitoring of treated syphilis patients. IMPORTANCE Syphilis remains a public health problem; therefore, health systems must incorporate screening tools that allow a rapid and accurate diagnosis to provide adequate treatment. The DPP Syphilis Screen & Confirm Assay simultaneously detects treponemal and nontreponemal antibodies, emerging as an alternative for identifying cases in situations in which there is no infrastructure to perform conventional syphilis testing, but it is necessary to generate evidence regarding the performance of this technology in various scenarios. We found that the test performs well, compared to TPPA and RPR tests, using stored samples from participants at high risk of acquiring syphilis. Additionally, when the Chembio microreader was incorporated, similar results are obtained by the device, compared to those reported by trained laboratory professionals, and correlated with the semiquantitative results of the RPR test. We think that the use of the DPP Syphilis Screen & Confirm Assay with the microreader might help in detecting active syphilis cases and perhaps in monitoring treatment responses in the field.

Bridging the gap between development of point-of-care nucleic acid testing and patient care for sexually transmitted infections

The incidence rates of sexually transmitted infections (STIs), including the four major curable STIs - chlamydia, gonorrhea, trichomoniasis and, syphilis - continue to increase globally, causing medical cost burden and morbidity especially in low and middle-income countries (LMIC). There have seen significant advances in diagnostic testing, but commercial antigen-based point-of-care tests (POCTs) are often insufficiently sensitive and specific, while near-point-of-care (POC) instruments that can perform sensitive and specific nucleic acid amplification tests (NAATs) are technically complex and expensive, especially for LMIC. Thus, there remains a critical need for NAAT-based STI POCTs that can improve diagnosis and curb the ongoing epidemic. Unfortunately, the development of such POCTs has been challenging due to the gap between researchers developing new technologies and healthcare providers using these technologies. This review aims to bridge this gap. We first present a short introduction of the four major STIs, followed by a discussion on the current landscape of commercial near-POC instruments for the detection of these STIs. We present relevant research toward addressing the gaps in developing NAAT-based STI POCT technologies and supplement this discussion with technologies for HIV and other infectious diseases, which may be adapted for STIs. Additionally, as case studies, we highlight the developmental trajectory of two different POCT technologies, including one approved by the United States Food and Drug Administration (FDA). Finally, we offer our perspectives on future development of NAAT-based STI POCT technologies.

Sexually Transmitted Infections Treatment Guidelines, 2021

These guidelines for the treatment of persons who have or are at risk for sexually transmitted infections (STIs) were updated by CDC after consultation with professionals knowledgeable in the field of STIs who met in Atlanta, Georgia, June 11–14, 2019. The information in this report updates the 2015 guidelines. These guidelines discuss 1) updated recommendations for treatment of Neisseria gonorrhoeae, Chlamydia trachomatis, and Trichomonas vaginalis; 2) addition of metronidazole to the recommended treatment regimen for pelvic inflammatory disease; 3) alternative treatment options for bacterial vaginosis; 4) management of Mycoplasma genitalium; 5) human papillomavirus vaccine recommendations and counseling messages; 6) expanded risk factors for syphilis testing among pregnant women; 7) one-time testing for hepatitis C infection; 8) evaluation of men who have sex with men after sexual assault; and 9) two-step testing for serologic diagnosis of genital herpes simplex virus. Physicians and other health care providers can use these guidelines to assist in prevention and treatment of STIs.

An old disease on the rise: new approaches to syphilis in pregnancy

PURPOSE OF REVIEW

Maternal and congenital syphilis infection is on the rise in the United States and worldwide. Without adequate testing or provider recognition of infection, treatment can be neglected resulting in significant perinatal morbidity and mortality. This review article discusses the epidemiology of T. pallidum, describes novel diagnostic tests, and considers the need to expand therapeutic options.

RECENT FINDINGS

A new chemiluminescence immunoassay for use in the reverse-sequence algorithm is more sensitive and specific in pregnant women than previously noted and is helpful for identifying pregnant women at highest risk for neonatal congenital syphilis. Point-of-care testing may be used to detect early syphilitic disease and provide same-day testing and treatment. Randomized control trials of oral cefixime for treatment of syphilis are paving the way for potential use in pregnant women. Penicillin skin testing, challenge, and desensitization in pregnancy can be done safely.

SUMMARY

Congenital syphilis is a preventable disease and treatable infection in the modern world, but we are still met with challenges in its eradication. We should proceed with advancing efficient laboratory testing, expanding medical therapy, and implementing public health measures to curb the rise of the disease.

Point-of-Care Testing for Sexually Transmitted Infections: A Review of Recent Developments

CONTEXT.—

Sexually transmitted infections (STIs) are among the most common communicable diseases globally and are associated with significant morbidity and mortality worldwide. Point-of-care tests have the potential to revolutionize the prevention and control of STIs by enabling rapid diagnosis and early treatment of infections, thus interrupting transmission and preventing the sequelae of untreated infections. Currently, there are several point-of-care (POC) tests available for the diagnosis of Treponema pallidum, Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis infections, although these tests differ with regard to their performance, turnaround time, and cost.

OBJECTIVE.—

To provide an updated review of the POC tests available and under development for the diagnosis of T pallidum, C trachomatis, N gonorrhoeae, and T vaginalis infections, to discuss the context for which these tests might be used, and to highlight future directions for test development.

DATA SOURCES.—

We reviewed the literature pertaining to the recent development and performance evaluations of POC tests for the diagnosis of syphilis, chlamydia, gonorrhea, and trichomonas.

CONCLUSIONS.—

Recently, there has been rapid development of new POC tests for STIs. Although there are inexpensive, rapid, and accurate POC tests available for syphilis, there are few such tests available for the diagnosis of chlamydia, gonorrhea, or trichomonas, and currently none with the ability to detect antimicrobial resistance in N gonorrhoeae. Research evaluating implementation strategies for the currently available tests and the development of additional POC tests that are rapid, accurate, and affordable are urgently needed to address the rising number of STIs worldwide.