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An enzyme
immunoassay for the serological detection of syphilis performed well
on samples collected from patients during all stages of disease.
Evaluation of an
enzyme immunoassay technique for detection of antibodies against Treponema
pallidum.
Castro R, Prieto ES, Santo I, Azevedo
J, da L. Exposto F.
Journal of Clinical
Microbiology 2003;41:250-253.
Summary:
Question
How well does an ELISA assay perform compared to a microhemagglutination
assay and the fluorescent treponemal antibody absorption test for the
detection of IgM and IgG antibodies to T. pallidum?
Design
This study describes a direct comparison of anti-T. pallidum IgG
and IgM ELISA assays with a microhemagglutination assay (MHA-TP) and a
fluorescent treponemal antibody absorption assay (FTA-Abs) for the
laboratory diagnosis of syphilis.
Participants
Four hundred forty-one patients attending an STD clinic in Lisbon,
Portugal, were tested, including 25, 25, 179, 105, and 107 patients with
primary, secondary, latent, treated, and no history of syphilis,
respectively.
Description of Tests and Diagnostic
Standard
All samples were analyzed for T. pallidum antibodies by the RPR
(Marco-Vue, Becton Dickinson), MHA-TP (Phasyl 210), FTA-Abs IgG and IgM (Euroimmune),
and enzyme immunoassay (Eti-syphilis-G and Eti-syphilis-M, DiaSorin) tests
according to the instructions of the manufacturers. For the ELISA assay,
IgG and IgM antihuman monoclonal antibodies were used to differentiate
between T. pallidum IgG and IgM antibodies. The cutoff point
between a positive and negative result was set at the absorbance of the
low-titer positive control. Samples with an absorbance within 10% of the
low-titer positive control were retested. Samples with different results
by the 4 techniques were retested.
Main Outcome Measures
The sensitivity and specificity of the RPR, MHA-TP, and IgG ELISA assays
in comparison to the FTA-Abs test were calculated by patient group.
Main Results
Among the 441 samples tested, 289 (65.5%), 313 (71%), 324 (73.5%), and 322
(73%) samples were reactive by the RPR, MHA-TP, FTA-Abs, and ELISA tests,
respectively. The results of the ELISA IgG assay compared to the MHA-TP
and FTA-Abs tests are shown in Table 1. The sensitivity and specificity of
the RPR, MHA-TP, and IgG ELISA assays compared to the FTA-Abs test for
detection of T. pallidum antibodies in each patient group are shown
in Table 2. There were no significant differences between results of the
ELISA IgM and the FTA-Abs test for IgM performed on samples from patients
with primary, secondary, and latent syphilis. None of the samples from
patients with past treated syphilis were reactive by either test.
| Table 1.
Results of IgG ELISA, MHA-TP, and FTA-Abs serological tests for
syphilis on 441 samples |
| IgG
ELISA |
MHA-TP |
FTA-Abs |
Total |
| Reactive |
Nonreactive |
Reactive |
Nonreactive |
| Reactive |
313 |
9 |
322 |
0 |
322 |
| Nonreactive |
0 |
119 |
2 |
117 |
119 |
| Total |
313 |
128 |
324 |
117 |
441 |
| Table 2. Performance
of RPR, MHA-TP, and IgG ELISA compared to FTA-Abs by patient group |
| Syphilis
group |
RPR |
MHA-TP |
IgG
ELISA |
| Sensitivity |
Specificity |
Sensitivity |
Specificity |
Sensitivity |
Specificity |
| Primary |
92% |
|
88% |
|
100% |
|
| Secondary |
100% |
|
100% |
|
100% |
|
| Latent |
97.2% |
|
99.4% |
|
100% |
|
| Treated |
57.9% |
|
92.6% |
|
97.9% |
|
| None |
88.8% |
|
100% |
|
100% |
|
Authors' Conclusions
The high sensitivity and specificity of this
ELISA technique during all stages of syphilis, together with the fact that
it is a simple, objective, and easily automated method, make it a useful
screening test for syphilis.
Source of funding: None given
For correspondence: Rita Castro,
Unidade de Doencas Sexualmente Transmitidas, Centro de Malaria e outras
Doencas Tropicais, Instituto de Higiene e Medicina Tropical, Rua da
Junqueira 96, 1349-008, Lisbon, Protugal. E-mail address: ritacastro@ihmt.uni.pt.
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