(P403) Proportion of Treponema pallidum PCR-positive primary syphilis infections which are seronegative: a systematic review.

Background

Earlier detection of syphilis is needed to reduce infectiousness and transmission and improve control. PCR for Treponema pallidum is highly sensitive for detecting primary syphilis but in many settings is not widely available or used. The aim of this systematic review was to investigate what proportion of PCR-positive primary syphilis infections are seronegative for syphilis, when serology is performed at clinical presentation for primary syphilis.

Methods

We undertook a systematic review to identify studies of patients presenting with primary syphilis where PCR for T. pallidum was performed on the primary syphilis lesion and serology for syphilis on the same occasion. The review was conducted according to the PRISMA checklist. Three databases (Medline, Embase, PubMed) were searched from 1 January 2000 to 27 November 2022. Only studies published in English were included. The search terms used were: ‘primary syphilis’, ‘Treponema pallidum’, ‘polymerase chain reaction’, ‘PCR’, ‘nucleic acid amplification test’, ‘NAAT’. Medical subject headings (MeSH) were used where possible.

Results

Of 2,569 studies identified, 10 studies were included: 2 prospective, 7 retrospective and 1 mixed prospective and retrospective.

All studies were conducted in clinical/sexual health settings (Canada, Australia, UK, France, Czechia, Cuba). Across the 10 studies, there were a total of 1084 individuals who had T. pallidum positive primary lesions. This included 867 men: gender was not specified in 2 studies. A total of 1043 individuals with T. pallidum positive primary lesions had serology performed. Among these, 14% (147/1043) (95% CI: 12-16%) were negative by serology, ranging between 4% (4/108) (95% CI 1-9%) and 50% (51/102) (95% CI: 40-60%). Among studies where the anatomical site of the primary lesion was provided there were a total of 503 anogenital and 8 oral primary lesions that were T. pallidum PCR-positive.

Conclusion

Among patients with primary syphilis, a proportion will have PCR-confirmed primary infection when serology is negative. This proportion may vary depending on a number of factors. More widespread availability and appropriate testing with PCR for T. pallidum may improve detection of primary syphilis, resulting in earlier diagnosis.