Previous syphilis infection attenuates subsequent infection, study finds
A previous syphilis infection attenuates the manifestations of a subsequent infection with Treponema pallidum, the bacterium that causes syphilis.
“Previous syphilis may induce an acquired immune response that limits dissemination of T. pallidum to blood and cerebrospinal fluid during a subsequent episode of syphilis,” Christina M. Marra, MD, professor of neurology, adjunct professor of infectious disease and vice chair of academic affairs in the University of Washington School of Medicine’s department of neurology, told Healio. “A practical issue for clinicians is that persons with a new episode of syphilis are about half as likely to have neurosyphilis if they had syphilis before.”
For their study, which was published in Clinical Infectious Diseases, Marra and colleagues reviewed medical and public health records for 651 people with syphilis. They examined the total number of syphilis episodes for each patient and detected the presence of T. pallidum in the blood and rRNA via a PCR test. They defined an index episode of syphilis as the most recent syphilis episode for which the entry visit was initiated within 30 days of the patient’s syphilis diagnosis.
In total, 482 patients had one syphilis episode, 121 had two or more and 48 had three or more. The proportion of patients who had an index episode that was early latent stage was substantially higher among individuals with three or more syphilis episodes. The adjusted odds of T. pallidum detection in blood or rRNA at the index episode was significantly lower in patients who had previous syphilis (adjusted OR = 0.17; 95% CI, 0.09-0.31). Additionally, the aOR for neurosyphilis at the time of index episode was substantially lower in patients who had a previous syphilis in infection (aOR = 0.54; 95% CI, 0.34-0.87).
Marra said that it is possible that cases of latent syphilis were misclassified due to individuals without clinical findings of syphilis who were included.
“We repeated our analysis in people with clinical evidence of syphilis, in whom the syphilis diagnosis was not in doubt, and we came to the same conclusions,” Marra said. “Also, we weren’t able to provide a definitive answer to whether people who have had syphilis before are more likely to present with early latent syphilis than with primary or secondary syphilis when they have syphilis again. This is an area for future research.”