Utility of rapid plasmin reagin titres in assessing treatment response and re-infection for infectious syphilis
Ricky Harjanto A , Don E. Smith
A B E , Hamish Barratt , Melissa Kelly A C , Derek Chan A B , Virginia Furner A , Maggie Smith A , Amrita Ronnachit C , Jeffrey Post C and William Rawlinson D
A The Albion Centre, 150 Albion Street, Surry Hills, NSW 2010, Australia.
B School of Public Health & Community Medicine, University of New South Wales, High Street, Kensington, NSW 2033, Australia.
C Infectious Diseases Department, Prince of Wales Hospital, 320–346 Barker Street, Randwick, NSW 2031, Australia.
D Serology and Virology Division, NSW Health Pathology, Prince of Wales Hospital, 320–346 Barker Street, Randwick, NSW 2031, Australia.
E Corresponding author. Email: don.smith@health.nsw.edu.au
Sexual Health 17(4) 330-336 https://doi.org/10.1071/SH20043
Submitted: 31 March 2020 Accepted: 15 May 2020 Published: 21 July 2020
Abstract
Background: The rapid plasma reagin (RPR) assay is commonly used as a surrogate marker of infectious syphilis, but is non-specific, slow to change and variable in its rate of decline post treatment. Methods: Within an urban sexual health service testing predominantly men who have sex with men, a file review of RPR changes was undertaken in all subjects who had a dilution level of ≥1 : 4, between January 2015 to the end of December 2018. Results: Overall, 248 cases of infectious syphilis were identified in 215 subjects (165 HIV seropositive, 50 HIV seronegative). Among unique-subject cases with follow-up RPR recorded, seroreversion to a non-reactive titre was achieved in only 42.3% (71/168) cases at a median of 235 days (interquartile range: 138–348 days) and was significantly less likely if patients had HIV infection (P = 0.02), late latent syphilis (P = 0.003) or a subsequent syphilis infection (P < 0.0001). Having HIV infection (P = 0.03) or a subsequent episode of syphilis (P = 0.01) were associated with a lower likelihood of documented cure. Conclusions: The slow decay in RPR titres post therapy and the inability of a significant number of subjects to achieve a non-reactive result over time makes RPR a poor test for assessing the adequacy of treatment or in diagnosing re-infection, especially in populations having repeated and frequent risk exposures. As the number of syphilis cases continue to climb, better tests that accurately assess pathogen presence are urgently needed.
Additional keywords: HIV, men who have sex with men, serology, seroreversion, Treponema pallidum.
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