Analytical performance characteristics of a new transcription-mediated amplification assay for Treponema pallidum.

Getman, Damon; Lin, Mike; Barakat, Nesreen; Skvoretz, Rhonda; Godornes, Charmie; Swenson, Paul; Nenninger, Ashley; Golden, Matthew R; Lukehart, Sheila A

This study evaluated the performance characteristics of a new research use transcription-mediated amplification (TMA) assay for detection of ribosomal RNA from Treponema pallidum (Tp). Analytical sensitivity determined using dark field quantitated Tp was 1.4 organisms/ml (95% CI: 0.7-6.33). Dilution of Tp IVT RNA in STM yielded 100% positivity (n=3) at 10 copies/ml (4 copies/reaction). Analytical specificity testing of non-target microorganisms (N=59), including the closely related non-syphilis treponemes T. denticola and T. phagedenis, yielded 0% positivity. TMA testing of mucosal swab specimens collected from men who have sex with men (MSM) attending a sexually transmitted disease clinic yielded 1.8% (17/944) TMA positive results. A collection of 56 serum specimens obtained from a separate cohort of patients with known rapid plasma reagin (RPR) status and syphilis clinical diagnosis were 19.6% (11/56) TMA positive overall, 29.7% (11/37) positive among subjects with syphilis diagnosis, including 8 (36.3%) of 22 persons with primary or secondary syphilis, 2 (20%) of 10 persons with early latent syphilis and 1 (20%) of 5 persons with late latent or unstaged syphilis. None (0%) of 18 RPR positive sera from patients with a history of treated syphilis was TMA positive. These results show TMA is an analytically sensitive and specific method for detection of Tp rRNA and is compatible with serum specimens in addition to pharyngeal and rectal mucocutaneous swab specimens. Automated real time TMA testing for T. pallidum may be useful as an adjunctive method with serology for screening and diagnostic testing of selected patient populations for syphilis.