Which algorithm should be used to screen for syphilis? Curr Opin Infect Dis. 2012;25:79-85. [PMID: 22156894 DOI: 10.1097/qco.0b013e32834e9a3c]

Point of care diagnostics for sexually transmitted infections: perspectives and advances

Accurate and inexpensive point-of-care (POC) tests are urgently needed to control sexually transmitted infection epidemics, so that patients can receive immediate diagnoses and treatment. Current POC assays for Chlamydia trachomatis and Neisseria gonorrhoeae perform inadequately and require better assays. Diagnostics for Trichomonas vaginalis rely on wet preparation, with some notable advances. Serological POC assays for syphilis can impact resource-poor settings, with many assays available, but only one available in the U.S. HIV POC diagnostics demonstrate the best performance, with excellent assays available. There is a rapid assay for HSV lesion detection; but no POC serological assays are available. Despite the inadequacy of POC assays for treatable bacterial infections, application of technological advances offers the promise of advancing POC diagnostics for all sexually transmitted infections.

Syphilis detection using the Siemens ADVIA Centaur Syphilis treponemal assay

BACKGROUND

Treponemal tests for detecting syphilis should be sufficiently sensitive and specific, especially when used as the first-line method in reverse-algorithm testing. We compared the Siemens ADVIA Centaur® Syphilis assay to 2 other commercial assays in use by the Star-MDC laboratory to evaluate its performance and usability.

METHODS

Agreement between the Siemens ADVIA Centaur Syphilis assay, Siemens IMMULITE® 2000 Syphilis Screen, and Biokit bioelisa Syphilis 3.0 assay was evaluated using 1251 patient samples (50 from known positives, 701 from patients referred for syphilis testing, and 500 from pregnant women). Reactive samples (i.e., reactive according to at least two of the three treponemal methods) were further evaluated using Western blot IgG and IgM, and Venereal Disease Research Laboratory (VDRL) testing.

RESULTS

Overall, positive and negative agreement was 100% between the Centaur and IMMULITE assays. In this study, overall agreement was 99.92% between either of the Siemens assays and the Biokit assay; positive agreement was 99%, and negative agreement was 100%. Overall, 0.88% (11/1251) of the samples were interpreted as positive/reactive based on the combined positive results by the ADVIA Centaur, IMMULITE 2000, and bioelisa assays; a positive Euroline anti-Treponema pallidum IgM blot; and a VDRL result of ≥1:8. In this study, no false-reactive samples were identified using this method.

CONCLUSION

The Centaur Syphilis assay performance is comparable to the other 2 commercial assays.

False-positive rapid plasma reagin testing in patients with acute Plasmodium vivax malaria: a case control study

Non-treponemal tests such as the rapid plasma reagin (RPR) assay are mainstays of syphilis diagnosis, but false-positive tests are common. We identified false-positive RPR titers in 8.2% of patients with malaria due to Plasmodium vivax in northern Peru. Similar rates were not detected in patients with other acute febrile illnesses.

A comparison of the analytical level of agreement of nine treponemal assays for syphilis and possible implications for screening algorithms

OBJECTIVE

The serological diagnosis of syphilis requires the detection of two distinct antibodies, the non-treponemal and trepomenal. Center for Disease Control and Prevention (CDC) recommends screening first with a non-treponemal test such as (Rapid Plasma Reagin/Venereal Disease Research Laboratory), and then confirming those results with one of the several treponemal tests (Fluorescent Treponemal Antibody-Absorption (FTA-ABS), Enzyme Immunoassay, chemiluminescence, treponema pallidum particle agglutination (TP-PA) or Point of Care). Owing to the high volume of samples processed by some laboratories using automated systems, the screening with treponemal assays and confirming with non-treponemal tests is becoming the established norm. The purpose of this study was to evaluate eight treponemal assays using TP-PA as the predicate assay.

METHODS

290 stored serum samples were tested qualitatively according to the manufacturer's directions.

RESULTS

Concordance with specimens tested as reactive or non-reactive using TP-PA was: FTA-ABS 94.5-100%, Trep-Sure 100-98.9%, BioELISA 100-98.9%, INNO-LIA 99.1-99.4%, BIOLINE 100-98.9%, CAPTIA IgG 100-97.2%, Trep-ID 100-100% and LIAISON 100-99.4%. In order to properly evaluate the performance of these assays, the analytical sensitivity was determined by endpoint titration of serial dilutions of the reactive serum samples in normal sera. The median endpoint titre varied from 1:4 for FTA-ABS to 1:512 for Trep-Sure.

CONCLUSIONS

The performance of the treponemal serological assays was comparable while using medium and high-titre sera. However, the varying performance on specimen dilutions suggests that there may be differences in sensitivity with low-titre sera that are more prevalent in primary and late syphilis cases.

Usefulness in clinical practice of a point-of-care rapid test for simultaneous detection of nontreponemal and Treponema pallidum-specific antibodies in patients suffering from documented syphilis

The usefulness of a point-of-care immunochromatographic dual test for the simultaneous detection of both nontreponemal and Treponema pallidum-specific antibodies (Chembio Diagnostics Systems Inc., Medford, NY, USA) was assessed in various situations related to syphilis, by reference to conventional syphilis serology. Thawed sera were obtained from 100 adults including 36 primary syphilis, 6 secondary syphilis, 6 re-infection, 9 recently-treated syphilis, and 43 old syphilis. Doubtful reactivities for the treponemal line were considered positive; doubtful reactivities for the nontreponemal line were considered positive only when the treponemal line was present. The sensitivity, the specificity, and its concordance to gold standard serology of treponemal line were high, around 90%. The sensitivity of nontreponemal line was 96.3%, its specificity 76.7%, and its concordance 83.4%. In conclusion, the dual rapid test from Chembio Diagnostics Systems Inc. is useful for rapid point-of-care diagnosis in the various situations encountered with patients suffering from syphilis.

Comparing the performance of traditional non-treponemal tests on syphilis and non-syphilis serum samples

The goal of the present study was to determine the performance of two traditional non-treponemal tests for syphilis. Syphilis sera (n = 209) included different stages of disease, and control sera (n = 247) were from patients with tumours, leprosy, systemic lupus erythematosus, hepatitis, pregnant women and healthy individuals. Treponema pallidum ELISA, Treponema pallidum particle agglutination and rapid treponema-specific tests were used as gold standards. Rapid plasma reagin or toluidine red unheated serum test had a sensitivity and specificity of over 95%. False-negative reactions of rapid plasma reagin and toluidine red unheated serum test were observed mainly in primary and latent syphilis cases, and false-positive reactions were present in systemic lupus erythematosus, hepatitis-infected patients. Overall, both non-treponemal tests had high sensitivities and specificities making the assays attractive as screening tests for syphilis. When examined on WHO reference serum samples and based on lower limits of detection, non-treponemal tests were less sensitive than treponema-specific tests.

Characterization of sera with discordant results from reverse sequence screening for syphilis

Reverse sequence screening for syphilis (RSSS) (screening with treponemal tests, followed by confirmation with nontreponemal tests) has been increasingly adopted. CDC recommends confirmation of discordant results (reactive EIA/CIA and nonreactive nontreponemal test) with Treponema pallidum particle agglutination assay (TP-PA). We characterized sera with discordant results from RSSS with Architect Syphilis TP CIA. Among 15,713 screening tests using Architect Syphilis TP at Seoul National University Gangnam Center between October 2010 and May 2011, 260 (1.7%) showed reactive results. Rapid plasma reagin (RPR) and TP-PA were performed on 153 available sera among them. On sera with discordant results between Architect Syphilis TP and TP-PA, INNO-LIA Syphilis Score and FTA-ABS were performed. Among 153 sera, RPR was nonreactive in 126 (82.4%). Among them, TP-PA was positive in 103 (81.7%), indeterminate (±) in 7 (5.6%), and negative in 16 (12.7%). Out of 16 CIA(+)/RPR(-)/TP-PA(-) sera, INNO-LIA Syphilis Score and/or FTA-ABS were negative on 14 sera. Out of 7 CIA(+)/RPR(-)/TP-PA(±) sera, INNO-LIA Syphilis Score and FTA-ABS were positive/reactive in 6 sera. RSSS with confirmation by TP-PA on sera with discordant results between Architect Syphilis TP and RPR effectively delineated those discordant results and could be successfully adopted for routine checkup for syphilis.

A dual point-of-care test shows good performance in simultaneously detecting nontreponemal and treponemal antibodies in patients with syphilis: a multisite evaluation study in China

BACKGROUND

Rapid point-of-care (POC) syphilis tests based on simultaneous detection of treponemal and nontreponemal antibodies (dual POC tests) offer the opportunity to increase coverage of syphilis screening and treatment. This study aimed to conduct a multisite performance evaluation of a dual POC syphilis test in China.

METHODS

Participants were recruited from patients at sexually transmitted infection clinics and high-risk groups in outreach settings in 6 sites in China. Three kinds of specimens (whole blood [WB], fingerprick blood [FB], and blood plasma [BP]) were used for evaluating sensitivity and specificity of the Dual Path Platform (DPP) Syphilis Screen and Confirm test using its treponemal and nontreponemal lines to compare Treponema pallidum particle agglutination (TPPA) assay and toluidine red unheated serum test (TRUST) as reference standards.

RESULTS

A total of 3134 specimens (WB 1323, FB 488, and BP 1323) from 1323 individuals were collected. The sensitivities as compared with TPPA were 96.7% for WB, 96.4% for FB, and 94.6% for BP, and the specificities were 99.3%, 99.1%, and 99.6%, respectively. The sensitivities as compared with TRUST were 87.2% for WB, 85.8% for FB, and 88.4% for BP, and the specificities were 94.4%, 96.1%, and 95.0%, respectively. For specimens with a TRUST titer of 1:4 or higher, the sensitivities were 100.0% for WB, 97.8% for FB, and 99.6% for BP.

CONCLUSIONS

 DPP test shows good sensitivity and specificity in detecting treponemal and nontreponemal antibodies in 3 kinds of specimens. It is hoped that this assay can be considered as an alternative in the diagnosis of syphilis, particularly in resource-limited areas.