Analytical evaluation of nine serological assays for diagnosis of syphilis

Evaluating the diagnostic accuracy of TpN17 and TmpA recombinant proteins in syphilis detection: a phase II study

Syphilis is a sexually transmitted infection (STI) caused by the spiral bacterium Treponema pallidum. Diagnosis is based on epidemiology, clinical and serology, but serodiagnosis is challenging because distinct clinical forms of the infection may influence serological performance. Several recombinant Treponema pallidum-proteins have already been tested for syphilis diagnosis and they are critical to achieve high accuracy in serological testing. A total of 647 samples were included in the study: 180 T. pallidum-positive samples, 191 T. pallidum-negative samples and 276 sera from individuals infected with unrelated diseases. The diagnostic potential was validated by analysis of ROC curves. For the indirect ELISA, TpN17 (100%) and TmpA (99%) showed excellent AUC values. Sensitivity values were 97.2% for TpN17 and 90.6% for TmpA, while specificity was 100% for both molecules. According to the clinical phase, TmpA ranged from 84% to 97%, with the highest value for secondary syphilis. TpN17 was 100% sensitive for the primary and secondary stages and 93.2% for recent latent syphilis. All clinical phases achieved 100% specificity. Accuracy values showed that TmpA (> 95%) and TpN17 (> 98%) presented high diagnostic accuracy for all clinical stages of syphilis. Cross-reactivity was only observed in one sample positive for Chagas disease (1.5%), when TpN17 was evaluated. On the other hand, TmpA showed reactivity for two samples positive for Chagas disease (3.1%), one sample positive for HBV (1.25%), two samples positive for HIV (9.5%) and one sample positive for HTLV (1.6%). The TmpA antigen's performance was evaluated in multiple studies for syphilis diagnosis, corroborating our findings. However, TpN17 sensitivity values have ranged in other studies. According to clinical stages of the infection, our findings obtained close performance values.

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.

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.

The Traditional or Reverse Algorithm for Diagnosis of Syphilis: Pros and Cons

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.

Syphilis Laboratory Guidelines: Performance Characteristics of Nontreponemal Antibody Tests

We reviewed the relevant syphilis diagnostic literature to address the following question: what are the performance characteristics, stratified by the stage of syphilis, for nontreponemal serologic tests? The database search included key terms related to syphilis and nontreponemal tests from 1960–2017, and for data related to the venereal disease research laboratory test from 1940–1960. Based on this review, we report the sensitivity and specificity for each stage of syphilis (primary, secondary, early latent, late latent, or unknown duration; tertiary as well as neurosyphilis, ocular syphilis, and otic syphilis). We also report on reactive nontreponemal tests in conditions other than syphilis, false negatives, and automated nontreponemal tests. Overall, many studies were limited by their sample size, lack of clearly documented clinical staging, and lack of well-defined gold standards. There is a need to better define the performance characteristics of nontreponemal tests, particularly in the late stages of syphilis, with clinically well-characterized samples. Published data are needed on automated nontreponemal tests. Evidence-based guidelines are needed for optimal prozone titrations. Finally, improved criteria and diagnostics for neurosyphilis (as well as ocular and otic syphilis) are needed.

2020 European guideline on the management of syphilis

The 2020 edition of the European guideline on the management of syphilis is an update of the 2014 edition. Main modifications and updates include: -The ongoing epidemics of early syphilis in Europe, particularly in men who have sex with men (MSM) -The development of dual treponemal and non-treponemal point-of-care (POC) tests -The progress in non-treponemal test (NTT) automatization -The regular episodic shortage of benzathine penicillin G (BPG) in some European countries -The exclusion of azithromycin as an alternative treatment at any stage of syphilis -The pre-exposure or immediate post-exposure prophylaxis with doxycycline in populations at high risk of acquiring syphilis.

Comparison of "Lumipulse anti-Treponema pallidum" and "Architect Syphilis TP" and further examination

Background

Syphilis is a sexually transmitted disease caused by Treponema pallidum (TP) infection. In recent years, diagnostic reagents with fully automated immunoassay instruments have become mainstream. However, these positive screening tests with high sensitivity, which are performed with full automation, need confirmation by Treponema pallidum particle agglutination (TPPA) to be judged as positive.

Methods

We evaluated the diagnostic performance of Lumipulse G TP‐N assay (Lumi‐TP, Fujirebio Inc) in 223 preselected TP‐positive samples and 1041 TP‐negative samples, compared it with that of the TP gold standard test (TPPA) and Architect Syphilis TP test (Archi‐TP, Abbott).

Results

The concordance rates for the results for the positive and negative samples between Lumi‐TP and TPPA were 100%. On the other hand, the rates for the results between Archi‐TP and TPPA were 100% for positive samples and 99.14% (1032/1041) for negative samples. Correlation tendency and rate between Archi‐TP and Lumi‐TP were 2.549 and 0.841 in positive specimens up to 160 detected values in Lumi‐TP. However, the detection value of Archi‐TP reached a plateau when it exceeded about 40. Furthermore, according to the comparison of each value obtained from Archi‐TP and Lumi‐TP with the strength of the staining of each line in the immune‐chromatography assay kit, ESPLINE TP (Fujirebio Inc) for TP major antigens, Tp15‐17 and TpN47, it was found that Lumi‐TP obtained higher values than Archi‐TP, particularly for TpN 47.

Conclusions

Lumi‐TP has high specificity and is useful not only for screening but also for determining the amount of anti‐TP antibodies.

An electrochemical scaffold sensor for rapid syphilis diagnosis

The faster a disease can be diagnosed, the sooner effective treatment can be initiated, motivating a drive to replace standard laboratory techniques with point-of-care technologies that return answers in minutes rather than hours. Thus motivated, we describe the development of an E-DNA scaffold sensor for the rapid and convenient measurement of antibodies diagnostic of syphilis. To achieve this (and in contrast to previous sensors of this class, which relied on single, linear epitopes for detection), we utilized a near full-length antigen as the sensor's recognition element, allowing us to simultaneously display multiple epitopes. The resultant sensor is able to detect antibodies against Treponema pallidum pallidum, the causative agent of syphilis, at clinically relevant concentrations in samples in less than 10 min. Preliminary results obtained using sero-positive and sero-negative human samples suggest the clinical sensitivity and specificity of the approach compare well to current gold-standard tests, while being simple and rapid enough to deploy at the point of care.

Economic Assessment of Reverse Algorithm Syphilis Screening in a High Prevalence Population

BACKGROUND

More laboratories are screening for syphilis with automated treponemal immunoassays. We compared direct costs and downstream consequences when a local public health laboratory switches from a traditional algorithm (nontreponemal screening) to a reverse algorithm (treponemal screening).

METHODS

We created a decision analysis model based on laboratory and surveillance data to estimate the cost-effectiveness of a reverse syphilis-screening algorithm from the perspectives of the Los Angeles County Public Health Laboratory and the Los Angeles County Department of Public Health (laboratory + STD Program costs) in 2015 US dollars.

RESULTS

The estimated total costs for the Department (Public Health Laboratories) were $2,153,225 ($367,119) for the traditional algorithm and $2,197,478 ($239,855) for the reverse algorithm. Reverse algorithm screening was estimated to detect an additional 626 cases of syphilis, 9.7% more than the traditional algorithm. The incremental cost-effectiveness ratio for the reverse algorithm from the Public Health Department's perspective was $39 per additional syphilis case detected. Cost of follow-up, screening test costs, positivity rates, and frequency of repeat infections most affected the cost-effectiveness of reverse algorithm. Costs were significantly higher for the reverse algorithm when the enzyme Immunoassay/chemiluminescence immunoassay screening test cost was the same as the published Centers for Medicaid Services treponemal test cost.

CONCLUSIONS

Using the reverse algorithm would have been slightly more expensive for the Los Angeles County Department of Public Health, but would have identified more syphilis cases and would have resulted in lower laboratory costs.

TPPA titer as a new adaptation for early diagnosis of congenital syphilis: a retrospective analysis of observation over three years in Yunnan, China

Background

Early diagnosis of congenital syphilis (CS) is difficult. This study aimed to determine the serological response discipline of syphilis passive antibody (SPA) in infants born to mothers with syphilis and provide the basis for the early diagnosis of CS.

Methods

Thirty-three infants born to mothers with syphilis and six infants with CS were recruited. The toluidine red unheated serum test (TRUST) and Treponema pallidum particle agglutination (TPPA) titers were followed up after birth.

Results

The results showed that serological response in the serum of infants with the TPPA titer decreased threefold at 3rd month, or the titer dropped to a minimum of 1:40 at 9th month was SPA. The TPPA titer of 6 CS cases remained positive after 3-year follow-up, and the titer did not decline after treatment and maintained longer. The infants with TRUST titer ≥ 1:4 at birth were prone to become syphilis serofast, while TRUST titer < 1:4 turned to negative quickly.

Conclusion

In infants with SPA, the TRUST converted negative earlier than the TPPA. The lower the TPPA initial titer was, the shorter the seroreversion time required. The TPPA titer can be used to predict CS in infants born to mothers with syphilis.

Comparing three treponemal tests for syphilis screening

We compared the performance and ease of use for three high-throughput treponemal immunoassays: Phoenix Biotech Trep-Sure Total Antibody EIA, Siemens ADVIA® Centaur Syphilis Assay, and DiaSorin LIAISON® Treponema Assay. One thousand serum samples submitted for routine screening were used in this study. Each assay demonstrated comparable sensitivity, specificity, and percent agreement (98-100%) compared with Treponema pallidum particle agglutination (TP-PA). Thus, treponemal immunoassays are an acceptable alternative for syphilis screening or confirmatory testing. Batch sizes and technologist active time varied between each treponemal immunoassay; the chemiluminescence platforms offered significantly greater ability to batch (random access vs. fixed batch sizes) in less time. When we compared the results obtained using a reverse algorithm approach to those obtained using a traditional algorithm, we found that the reverse algorithm identified 38 additional seropositive individuals that were not detected using the traditional algorithm. Clinical evaluation was useful for resolving cases with discordant serology.

Serological Tests for Acquired Syphilis in Immuno-competent Patients

Serological tests represent a valuable tool for the diagnosis and monitoring the syphilis treatment. Non-treponemal antibodies are nonspecific to detect the infection, but antibody titers are used to monitor the effects of syphilis treatment. A definitive diagnosis of syphilis is made using treponemal tests, because they detect specific antibodies to the treponemal strains or treponemal fragments, which cause syphilis. These tests may remain reactive for years, sometimes for life, regardless of the therapy outcome. Even after successful treatment, approximately 85% of patients remain positive for treponemal antibodies for the rest of their lives. However, treponemal tests cannot differentiate past infections from a current infection. Therefore, we use a combination of specific and non-specific tests, the two most frequently used diagnostic algorithms. The traditional algorithm begins with a non-treponemal assay, and if it is positive, the treponemal test is done. A positive treponemal test indicates syphilis. The reverse serology algorithm detects early, primary, and treated syphilis that may be missed with traditional screening. However, non-treponemal test is necessary to detect patients with active syphilis.

Evaluation of the automated ADVIA centaur® XP syphilis assay for serological testing

We evaluated the performance of the ADVIA Centaur XP Syphilis assay (Siemens Healthcare Diagnostics, Tarrytown, NY, USA) using samples previously tested on the ARCHITECT i4000SR system (Abbott Diagnostics, Lake Forest, IL, USA) and confirmed by the Treponema pallidum particle agglutination assay (TPPA) (SERODIA-TPPA, Fujirebio Diagnostics Inc., Malvern, PA, USA). Clinical patient information was included to aid resolution of discordant samples where available. Precision, interference, and cross-reactivity were also assessed. Relative to patient clinical status, the sensitivity of both the ADVIA Centaur XP and the ARCHITECT assays was 100% (95% CI, 93.9-100), and the specificity of the ADVIA Centaur XP assay was 95.5% (95% CI, 90.4-98.3), which was slightly higher than that of the ARCHITECT assay at 93.9% (95% CI, 88.4-97.3). Overall agreement relative to patient clinical status was 96.9% (95% CI, 93.3-98.8) for the ADVIA Centaur XP assay and 95.8% (95% CI, 91.9-98.2) for the ARCHITECT assay. Overall agreement between the two automated assays was 96.9% (95% CI, 93.3-98.8). ADVIA Centaur XP assay precision was <5% at all index values tested. No significant interference was observed for lipemia or hemolysis; a small effect was seen with some samples for bilirubin. The assay exhibited no significant cross-reactivity with a number of potential interfering factors. The ADVIA Centaur XP Syphilis assay can be considered a sensitive and accurate assay for identification of treponemal antibodies in screening populations as well as patients presenting with suspicion of syphilitic infection.

Hepatitis B, HIV, and Syphilis Seroprevalence in Pregnant Women and Blood Donors in Cameroon

Objectives. We estimated seroprevalence and correlates of selected infections in pregnant women and blood donors in a resource-limited setting. Methods. We performed a cross-sectional analysis of laboratory seroprevalence data from pregnant women and voluntary blood donors from facilities in Cameroon in 2014. Rapid tests were performed to detect hepatitis B surface antigen, syphilis treponemal antibodies, and HIV-1/2 antibodies. Blood donations were also tested for hepatitis C and malaria. Results. The seroprevalence rates and ranges among 7069 pregnant women were hepatitis B 4.4% (1.1–9.6%), HIV 6% (3.0–10.2%), and syphilis 1.7% (1.3–3.8%) with significant variability among the sites. Correlates of infection in pregnancy in adjusted regression models included urban residence for hepatitis B (aOR 2.9, CI 1.6–5.4) and HIV (aOR 3.5, CI 1.9–6.7). Blood donor seroprevalence rates and ranges were hepatitis B 6.8% (5.0–8.8%), HIV 2.2% (1.4–2.8%), syphilis 4% (3.3–4.5%), malaria 1.9%, and hepatitis C 1.7% (0.5–2.5%). Conclusions. Hepatitis B, HIV, and syphilis infections are common among pregnant women and blood donors in Cameroon with higher rates in urban areas. Future interventions to reduce vertical transmission should include universal screening for these infections early in pregnancy and provision of effective prevention tools including the birth dose of univalent hepatitis B vaccine.