Rapid Diagnostic Tests for SyphilisA Preliminary Review of the U. S. Clinical Data

M Sutton, S Zackery, C Ciesielski, M Zajackowski, M Santana, C Langley, L Bernard, V Pope, M Fears, R Johnson, L Markowitz

Background Syphilis is diagnosed in the U.S. by a nontreponemal screening test and

a treponemal confirmatory test. on-site RPR plus offsite treponemal test, OR RPR and treponemal tests are sent offsite (turn-around time up to 1

week or more). Rapid immunochromatographic (ICS) diagnostic tests:

treponemal-based tests can provide results in 15 minutes may potentially be of use in non-traditional settings

Rapid ICS tests for syphilis are not FDA-cleared for use in the US. A U.S. based study was conceived to evaluate these rapid diagnostics

for syphilis.

Multi-site study of rapid diagnostic syphilis assays of persons attending STD clinics in

high syphilis morbidity areas

Cross-sectional study

3 ICS strips included vary by which Treponema pallidum antigens are present on the test band region

Two U.S. sites are currently evaluating the performance of 3 rapid diagnostic strips

ICS Strip

Immunochromatographic Strip (ICS)Rapid Diagnostics for Syphilis

Membrane strip based immunoassay

Test procedure Recombinant T. pallidum

antigen is coated on the test band region.

Sample is placed on application pad and reacts with antigen-colloidal gold conjugate.

If T. pallidum antibody is present an antigen-antibody-antigen gold complex will form (evident by line in the test area).

Line should always appear in control region.

I I

Application Test Control Absorbent Pad Line Line Pad

Positive Sample

Negative Sample

Interpretation of Results

Inconclusive

I

I I

Objectives

To evaluate ICS test performance using finger stick, whole blood, serum, and plasma specimens compared to RPR and TPPA

To compare ICS test performance with serum at local sites and CDC

To evaluate ICS test performance by syphilis stage of disease

Methods I

Enrollment- consenting adults age 18 or older

Finger stick done for point-of-care testing on 1 ICS test

Blood drawn for whole blood, serum, and plasma ICS testing at local sites and serum for CDC testing for 3 ICS tests

Data collection questionnaire includes clinical assessment of syphilis stage of disease, if applicable

Persons tested and treated for syphilis if needed according to established standard of care.

ICS tests are for investigational purposes only.

Methods II

Data analyzed using Epi-Info and SAS

Results reported by comparing to clinical standard of both RPR and TP-PA results

Sensitivity= positives/ RPR (+) TP-PA (+)

Specificity= negatives/RPR (-) TP-PA (-)

Syphilis case definitions

Results (Demographics)

N=383 64% male 47% African-American 32% White 18% Latino Reactive RPRs=24

Titers < 1:8=8 (33%) Titers ≥ 1:8=16 (67%) 20 4 24

21 338 359

41 342 383

TP-PAR NR

R

NRRPR

TOTAL

TOTAL

Results: Test performance (sensitivity)of ICS at local sites, by specimen type,

compared to RPR and TP-PA

Specimen Type

Sensitivity (%)Test 1 Test 2 Test 3

Whole Blood

100(17/17)

47.1(8/17)

82.4(14/17)

Serum 100(17/17)

76.5(13/17)

88.2(15/17)

Plasma 100(17/17)

75(12/16)

100(17/17)

Results: Test performance (specificity)of ICS at local sites, by specimen type,

compared to RPR and TP-PA

Specimen Type

Specificity (%)Test 1 Test 2 Test 3

Whole Blood

97.7(334/342)

99.7(336/337)

99.7(340/341)

Serum 93.3(319/342)

96.2(327/340)

99.1(339/342)

Plasma 93.2(313/336)

97.9(322/329)

99.1(331/334)

Results: Test Performance on Sera, Local Sites vs. CDC Laboratory,

compared to RPR and TPPA

0102030405060708090

100

Test 1 Test 2 Test 3 Test 1 Test 2 Test 3

LocalCDC

Sensitivity Specificity

Results: Point-of-care ICS (Finger stick) compared to RPR and TP-PA

Overall (any RPR titer and reactive TP-PA) Sensitivity=17/17 (100%) Specificity=324/327 (99.1%)

Clinical Diagnosis of Syphilis

Number of Cases

Primary 1Secondary 7Latent 9Previously treated(TP-PA (+) & RPR (-))

10

Conclusions

There is a broad range of sensitivities and specificities for the 3 ICS tests in whole blood, serum, and plasma.

Test performance for sera locally is very comparable to test performance at CDC.

The ICS point-of-care (finger stick) data show sensitivities of 100% and specificities of over 99%.

ICS tests are performing well to date with various stages of disease.

Limitations

Treponemal tests are unable to differentiate between active and previously treated syphilis.

Interval analysis only; more data needed.

Summary & Future Steps

Some rapid diagnostic tests show promising performance as screening tests for syphilis in the United States.

These ICS tests require few supplies and can potentially be used in both traditional clinical settings as well as non-traditional settings.

Data collection is ongoing.

Acknowledgments

S Zackery C Ciesielski M Zajackowski M Santana C Langley L Bernard V Pope M Fears R Johnson

L Markowitz J Braxton J Chapin J Lewis S Berman J Douglas B Litchfield CDC DASTLR Local Public Health Departments