Treponema pallidum Nucleic Acid Amplification Testing To Augment Syphilis Screening among Men Who Have Sex with Men

Abstract

Syphilis rates in much of the world are now at their highest levels in almost three decades, and new approaches to controlling syphilis, including diagnostic tests with shorter window periods, are urgently needed. We compared the sensitivity of syphilis serological testing using the rapid plasma reagin (RPR) test with that of the combination of serological testing and an experimental 23S rRNA Treponema pallidum real-time transcription-mediated amplification (TMA) assay performed on rectal and pharyngeal mucosal swabs. T. pallidum PCR assays for the tpp47 gene were performed on all TMA-positive specimens, as well as specimens from 20 randomly selected TMA-negative men. A total of 545 men who have sex with men (MSM) who were seen in a sexually transmitted disease clinic provided 506 pharyngeal specimens and 410 rectal specimens with valid TMA results. Twenty-two men (4%) were diagnosed with syphilis on the basis of positive RPR test results and clinical diagnoses, including 3 men with primary infections, 8 with secondary syphilis, 9 with early latent syphilis, 1 with late latent syphilis, and 1 with an unstaged infection. Two additional men were diagnosed based on positive rectal mucosal TMA assay results alone, and both also tested positive by PCR assay. At least 1 specimen was TMA positive for 12 of 24 men with syphilis (sensitivity, 50% [95% confidence interval [CI], 29 to 71%]). RPR testing and clinical diagnosis were 92% sensitive (95% CI, 73 to 99%) in identifying infected men. Combining mucosal TMA testing and serological testing may increase the sensitivity of syphilis screening in high-risk populations.

Analytical Performance Characteristics of a New Transcription-Mediated Amplification Assay for Treponema pallidum

“…The results presented in this report build on our prior work ( 13 ) and demonstrate the high analytical sensitivity and specificity of TMA for the detection of T. pallidum , especially the absence of cross-reactivity of the assay with nonsyphilis treponemes T. denticola and T. phagedenis and the ability to detect T. pallidum RNA in serum. The use of PCR-based NAATs as a direct detection method for syphilis has been reported on extensively, with several studies showing that these assays can detect T. pallidum in seronegative persons ( 8 – 12 , 24 , 25 ).…”

“…For the rectal and pharyngeal swab specimens, correlation of TMA-positive and -negative results with PCR, RPR serology, and clinical diagnosis of syphilis has been reported previously ( 13 ). Table 3 shows the agreement between TMA and T47 PCR assays for 75 of these swab specimens.…”

“…TMA-positive swab specimens, as well as swab specimens from 20 randomly selected patients with negative TMA test results, were also tested using a T. pallidum PCR assay for the single-copy-number T47 gene ( TP0574 ) ( 14 ). The results of this PCR testing were reported previously ( 13 ) in a companion study to the current investigation but are included in the present analysis in a revised format to provide for ready comparison within the context of the new analytical testing results. A convenience set of 56 remnant serum specimens with known rapid plasma reagin (RPR) results obtained from a separate cohort of clinic patients was tested by adding 0.5 ml of serum to a specimen transport tube containing 0.5 ml of Aptima urine transport medium (UTM), followed by the addition of 1.0 ml of Aptima STM prior to analysis on the Panther instrument.…”

“…As reported previously ( 13 ), deidentified residual rectal and pharyngeal specimens were obtained and prepared from 534 men who have sex with men (MSM) attending the Public Health—Seattle & King County (PHSKC) Sexual Health Clinic (SHC) from September to November 2017. The study was reviewed and approved by the University of Washington IRB, with an exemption from consent for testing remnant deidentified specimens.…”

“…A number of syphilis PCR assays have been developed, and studies have shown that as many as 27% of primary syphilis cases could be identified by PCR prior to seroconversion ( 8 – 12 ). Recently, we used an investigational transcription-mediated amplification (TMA) assay in a research study evaluating direct detection of T. pallidum rRNA by TMA in extragenital mucosal swabs, showing that TMA can sometimes detect syphilis in patients with negative serological results ( 13 ). Here, we present data on the analytical performance of this investigational real-time TMA assay, including analytical sensitivity, specificity, and interference.…”