Syphilis treatment outcomes in HIV-coinfected patients: a retrospective study

Background. The efficacy of antibiotic therapies used to treat syphilis in HIV-positive patients has not been sufficiently studied. In patients with coinfection, seronegativization of non-treponemal tests after syphilis therapy is often delayed, however, data on the reasons for the delayed serological response are limited and contradictory. Aim. To assess the frequency of syphilis treatment failure in HIV-positive patients and to identify factors affecting the development of serological resistance (SR). Methods. A post-hoc analysis of clinical, serological, liquorological and immunological data of 280 HIV-positive patients with syphilis who were under follow-up at St. Petersburg AIDS and Infectious Diseases Center has been conducted. Results. Syphilis treatment failure was observed in 44.1% of patients with coinfection. The risk of SR was higher in women (p = 0.002), in elder patients (p = 0.006), in those with a more advanced HIV infection (p = 0.017) and depended on the duration of syphilis before the treatment initiation (p 0.001). SR occurred more commonly after therapy for latent (p = 0.001), late syphilis (p 0.001), neurosyphilis (p = 0.014), and reinfections (p = 0.027). The lack of positive dynamics in microprecipitation reaction (MPR) with serum was mainly observed when the recommended treatment methods were not adhered to and when the therapy prescribed was insufficient for the relevant stage and form of syphilis (р = 0,012). The CD4+ T-lymphocyte count 350/μL increased the risk of SR 2.1-fold (p = 0.008). The occurrence of SR was not associated with ART, HIV RNA level (viral load), or pre-treatment MPR titer. Excessive doses of antibiotics during the initial treatment and additional therapy during the period of clinical and serological observation did not have a positive effect on the serological response. Conclusion. Due to the high frequency of syphilis treatment failure, HIV-infected patients require a careful choice of the initial treatment regimen combined with regular and prolonged clinical and serological follow-up.