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Higher RPR titers, recent diagnosis predict syphilis treatment response

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December 16, 2018

Higher rapid plasma reagin, or RPR, titers at diagnosis and a diagnosis made in more recent years are associated with serological treatment response in patients living with HIV who are diagnosed with early or late syphilis, according to study findings from Italy.

The study showed other predictors of treatment response for episodes of early syphilis, including higher nadir CD4+ count and a diagnosis of secondary syphilis, when compared with early latent syphilis. In patients diagnosed with late syphilis, treatment response also was associated with first infections.

The study also showed a significant increase in syphilis incidence in recent years, in line with other studies.

“In Western countries, there has been a resurgence of syphilis since 2000, with a peak prevalence in men who have sex with men (MSM) living with HIV,” Vincenzo Spagnuolo, MD, and colleagues from Vita-Salute San Raffaele University and the San Raffaele Scientific Institute, both in Milan, wrote.

According to the researchers, HIV infection has been associated with lower rates of serologically defined treatment response compared with those of the general population, though the research is conflicting, and studies have not defined predictors.

“Different guidelines have recommended the same treatment regimens for [people living with HIV] and the general population, regardless of the stage of syphilis; however, concerns regarding the treatment of syphilis in [people living with HIV] remain,” Spagnuolo and colleagues wrote.

They said many clinicians who care for patients with HIV continue to use three doses of benzathine penicillin G (BPG) to treat early syphilis because of concerns over lower efficacy of the recommended one-dose BPG regimen.

“Additionally, limited data are available on the efficacy of the alternative regimen, doxycycline, especially for the treatment of late latent syphilis,” they wrote. “Therefore, the aims of this study were to evaluate the rate of syphilis serological treatment response, in a large cohort of [people living with HIV], and to identify treatment response predictors (including different treatment regimens) in early and late stages of syphilis.”

For the study, Spagnuolo and colleagues defined serological treatment response as a fourfold or more decline in RPR titers or a reversion to nonreactive status 12 months following treatment for early syphilis and 24 months following treatment for late syphilis.

In all, 829 episodes of syphilis — 686 early and 143 late — in 564 patients were recorded at a Milan HIV clinic between January 2004 and June 2016. According to study findings, treatment response was observed in 88% (n = 732) of syphilis episodes, including 89% of early syphilis cases and 83% of late syphilis cases.

Spagnuolo and colleagues reported that treatment response in early syphilis cases was associated with a higher nadir CD4+ cell count, RPR titers greater than 1:32 at diagnosis, secondary syphilis, and cases of syphilis diagnosed in more recent years. In late syphilis cases, treatment response was more likely in first infections, cases occurring in more recent years, and RPR titers greater than 1:32 at diagnosis. They said treatment response in early or late syphilis did not depend on the type of regimen.

“Overall, subjects included in our study showed a good immune-virological status: at the time of diagnosis of syphilis, the median CD4+ cell count was approximately 600 cells/mm3, 81% had received some form of antiretroviral treatment and 80% of treated subjects had a viremia of less than 50 copies/mL,” the authors wrote. “Despite the fact that the three-dose BPG regimen remains the more frequently prescribed treatment, also among the early syphilis diagnoses, the one-dose BPG treatment has recently become the preferred regimen for treatment of early syphilis, in accordance with guidelines and recommendations.” – by Caitlyn Stulpin

Disclosures: The authors report no relevant financial disclosures.

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