Syphilis is a systemic sexually transmitted infection caused by the bacterium Treponema pallidum. The disease can be transmitted through sexual contact (person to person) or vertically from an infected mother to her unborn child.
Despite reaching its lowest rate in 2000-2001, incidences of syphilis have risen significantly since 2001. According to the 2022 CDC STI Surveillance Report, there were 207,255 reported cases of syphilis in the USA, marking the highest number since 1950 and representing an 80% increase from 2018.
In the traditional algorithm, testing begins with a non-treponemal test (RPR or VDRL); however, due to the lower specificity of these tests, a positive result requires confirmation with a treponemal test. This approach has the disadvantage of higher false-positive rates due to factors unrelated to syphilis.
This is why Aculabs will implement a reverse testing algorithm for syphilis detection.
The progression of syphilis is categorized into four stages:
Primary Stage: About three weeks after exposure, a non-painful skin lesion known as a chancre appears, often accompanied by regional lymphadenopathy.
Secondary Stage: This stage is characterized by the dissemination of Treponema pallidum, leading to general mucocutaneous lesions and widespread lymphadenopathy.
Latent Stage: Following the secondary stage, syphilis can enter a latent phase where the infection is subclinical and can only be detected through serological tests.
Tertiary Stage: Occurring in a minority of cases, this stage is marked by severe, progressive disease affecting various organs, which may manifest as cardiovascular syphilis, neurosyphilis, or gummatous syphilis.
An alternative approach, the reverse algorithm, starts with a treponemal test to detect specific antibodies to Treponema pallidum. If the treponemal test is positive, a non-treponemal test is then performed to assess disease activity and response to treatment. This method is more sensitive and specific for detecting both early and late stages of syphilis.
The CDC Sexual STD Treatment Guidelines recommend a two-step serological testing approach for the presumptive diagnosis of syphilis:
Treponeaml Tests: Treponemal tests detect antibodies specific to Treponema pallidum and confirm the presence of the infection. These tests include pallidum Passive Particle Agglutination (TP-PA) Assay and Chemiluminescence Immunoassays
Non-Treponemal Tests: Non-treponemal tests detect non-specific antibodies to cardiolipin, which are produced during acute syphilis. These tests can indicate active or past infection but have limitations due to potential false positives associated with various medical conditions, including other infections (e.g., HIV), autoimmune diseases, recent vaccinations, pregnancy, and older age. These include Venereal Disease Research Laboratory (VDRL) Test Rapid Plasma Reagin (RPR) Test
The implementation of the reverse algorithm will enhance the early detection and treatment of syphilis infections, ultimately helping to limit the spread of the disease. The process will involve:
- Initial Screening: Samples will be screened using a treponemal assay that employs chemiluminescent immunoassay technology on the LIAISON® Analyzer. This test detects both IgG and IgM antibodies to Treponema pallidum in human serum. The detection of IgM improves the sensitivity of early syphilis diagnosis, allowing detection up to 2 weeks earlier than IgG-only assays and up to 5-6 weeks earlier than non-treponemal assays.
- Follow-Up Testing:
- Negative Results: Samples that test negative by the screening assay do not require further testing and the patient is considered negative for syphilis.
- Positive Results: Samples that test positive are reflexed to the RPR test.
- If RPR is Reactive: The patient is considered positive for untreated or recently treated syphilis.
- If RPR is Non-Reactive: The sample is reflexed to a second treponemal test for further evaluation.
Early diagnosis of syphilis is crucial for preventing the spread of the disease and avoiding serious complications.
– Dr. Rita Khoury
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