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British Columbia's Experience after Implementation of the Treponema pallidum Reverse Algorithm and PCR Detection,
Muhammad Morshed1,2, Min-Kuang Lee1, Jonathan Laley1
1British Columbia Centre for Disease Control Public Health Laboratory, Vancouver, British Columbia, Canada.
Microbiology Spectrum
|June 6, 2022
Summary
The syphilis reverse screening algorithm in BC improved diagnosis, detecting over 4,600 late latent cases missed by older methods. Treponema pallidum PCR testing proved highly sensitive and crucial for monitoring antibiotic resistance.
Area of Science:
- Medical Diagnostics
- Infectious Diseases
- Public Health Surveillance
Background:
- British Columbia implemented a new syphilis reverse screening algorithm and Treponema pallidum PCR testing in 2014.
- The previous screening method involved initial testing with rapid plasma reagin (RPR).
- The new algorithm utilizes Siemens Advia Centaur syphilis assay (enzyme immunoassay [EIA]) for initial screening.
Purpose of the Study:
- To evaluate the performance characteristics of the syphilis reverse screening algorithm and PCR testing.
- To report on syphilis cases identified in British Columbia from 2015 to 2020.
- To assess the diagnostic sensitivity of PCR compared to traditional microscopy methods and monitor for antibiotic resistance.
Main Methods:
- Screening of 1,631,519 samples using EIA, with positive/equivocal results reflex tested by T. pallidum passive particle agglutination assay (TPPA) and RPR.
- Utilizing T. pallidum DNA PCR on clinical samples for direct detection and restriction fragment length polymorphism analysis for azithromycin resistance mutations.
- Obtaining case/epidemiological data from the BC surveillance system.
Main Results:
- The reverse algorithm detected 4,693 late latent syphilis cases potentially missed by RPR screening.
- PCR demonstrated high sensitivity (100%) compared to dark-field (52.9%) and immunofluorescence (52.4%) microscopy.
- Azithromycin resistance mutations A2058G (96%) and A2059G (4%) were identified in PCR-positive samples. Syphilis cases averaged 944-1,467 annually, predominantly in men reporting male sexual partners (62%).
Conclusions:
- The syphilis reverse algorithm exhibits a low false-positive rate and minimal equivocal results, effectively identifying previously undiagnosed late latent syphilis cases.
- PCR testing offers superior sensitivity for direct syphilis diagnosis over microscopy and is vital for tracking antimicrobial resistance.
- The implemented algorithm and PCR testing provide a comprehensive approach to syphilis surveillance and management in British Columbia.
