Background and problem The recent development and implementation of serological screening for syphilis using recombinant protein-based immunoassays has resulted in much confusion about the interpretation of positive results, particularly in low prevalence settings. Early experience suggests that a high proportion of positive tests are not confirmed by either non-treponemal or other treponemal tests. Many questions remain about the accuracy and relevance of these results.
Research needs We will discuss research questions related to the performance, utility, and effectiveness of these tests.
Performance of the existing tests Sensitivity, specificity, and positive predictive value in high- and low-prevalence populations. What gold standard should be used for evaluation of these tests?
Can performance of the existing tests be improved by simple modifications?
Reactivity in persons with past treated syphilis—how can this be determined?
Effectiveness of using the current tests for screening Does screening with the EIA tests result in the need for more additional, unnecessary testing? Does the delay in receiving prompt complete serological results result in delayed treatment and increased transmission of syphilis? How much unnecessary treatment results from the use of these tests for screening? What is the impact of EIA screening on public health time and dollars spent on contact tracing? What is the real cost of EIA screening, including the need for additional testing, possibility of additional transmission, and required public health follow-up?
Biological basis for the unconfirmed reactivity in the existing tests Which Treponema pallidum antigens are recognised by patient sera that are reactive only in the EIA tests?
Do such antisera have cross-reactivity with antigens of other treponemal species found in humans?
Next generation recombinant protein-based antibody tests Are there T pallidum-specific antigens? How can we identify them? Are there antigens for which antibody disappears or declines significantly following treatment?
Conclusions The increasingly widespread use of recombinant protein-based immunoassays has contributed to much confusion in serological testing for syphilis. Research efforts to understand the source of the problems with these first-generation tests are needed to provide clinicians with appropriate algorithms and tools to accurately and rapidly diagnose untreated syphilis in their patients.
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