P765 Added value oftreponema pallidumPCR in diagnosing early syphilis

Background Diagnosing an infection with Treponema pallidum, the causative agent of syphilis, is routinely based on serology. STD clinics routinely screen those with high-risk sexual behaviour, e.g. MSM, for syphilis. In case of an ulcus, swabs taken from the ulcer can be tested for T. pallidum by PCR. Here, we assessed the added value of PCR next to serology in primary syphilis. Methods Retrospective data were analysed from patients of our STI clinic. Samples were taken from the genital ulcer for T. pallidum PCR and syphilis serology was simultaneously performed. Serology was interpreted positive when seroconversion was detected or when RPR significantly increased in those with a history of treated syphilis. Serology was interpreted as negative when the screening was negative or when no significant rise in RPR was detected in those with a history of syphilis. Results In total 191 PCR – serology combined results were analysed. In total 70/191 (37%) PCRs were positive. In 24/70 (34%) samples the positive PCR result added to diagnosing primary syphilis, either because the serology was negative (n=5, 7.1%) and the diagnosis would have been missed or the positive PCR result added in staging syphilis (n=19, 27.0%) affecting the treatment regimen. Moreover in 11/76 (14%) serology positive patients the PCR was negative. Six of these patients were clinically diagnosed as primary syphilis, 3 as syphilis latens recens and 2 as syphilis stage unknown. Conclusion In our setting, the T. pallidum PCR is of added value in the diagnosis of primary syphilis as without PCR one in 10 early syphilis would have been missed and about one in 5 would have been possibly overtreated. Importantly, the PCR supports the low-threshold testing policy since patients can present within the window period of serology optimizing public health efforts to minimize transmission. Disclosure No significant relationships.