Background Treponema pallidum (TP) DNA has been detected in oral swabs from patients with early syphilis. The goal of this study was to determine the frequency of detectable TP DNA in oral swabs from patients with all stages of syphilis, and from appropriate controls.

Methods Blood (N = 131), oral swabs (N = 112) and lesion swabs (N = 72) were collected from 138 patients with untreated syphilis (cases). Controls were oral swabs collected from 89 patients presenting to an STD clinic for a concern other than syphilis, 59 HIV positive individuals, and 108 individuals 3, 6 or 12 months after treatment of uncomplicated or neurosyphilis (194 samples). DNA was extracted and underwent amplification of a portion of the TP tp0548 gene. Rapid plasma reagin (RPR) tests were performed on serum, and the association between RPR titer and oral TP detection assessed using Mann-Whitney U test.

Results Among those with known syphilis stage, TP was detected in oral swabs from 31/101 (31%) cases: 4/29 (14%) with primary, 20/49 (41%) with secondary, 6/15 (40%) with early latent, 1/7 (14%) with late latent syphilis, and 0/1 (0%) syphilis contact. Oral TP was detected in 18/74 (24%) without detectable blood TP, 6/18 (33%) without detectable lesion TP, and 21/78 (27%) without oral lesions. Oral TP detection was more likely with higher RPR titers (p = 0.002). Oral TP was not detected in any of the 342 control samples.

Conclusion Oral TP is detectable in patients at all syphilis stages, most commonly when serum RPR titer is high. Oral TP can be detected even when undetectable in blood or lesion swabs, and in the absence of oral lesions. While detection of DNA is not the same as detection of virulent organisms, these results suggest that individuals with syphilis could infect their partners solely through oral contact.

Disclosure No significant relationships.