Consequences of HIV/Syphilis Co-Infection on HIV Viral Load and Immune Response to Antiretroviral Therapy

Introduction: Although syphilis is a frequent co-infection in patients with human immunodeficiency virus (HIV) infection, the influence of syphilis on immune response and virologic failure in HIV-infected patients following initiation of antiretroviral therapy (ART) is not well-defined.

Methods: A retrospective study was conducted at Tianjin Second People's Hospital to evaluate the prevalence of syphilis and immune status in 4171 ART-naïve patients. The study included patients who initiated ART between August 2009 and June 2019.

Results: The prevalence of syphilis was 40.1% in all ART-naïve patients and 42.5% in ART-naïve men who have sex with men. HIV/syphilis co-infection was associated with higher virologic failure (odds ratio (95% confidence interval): 1.30 (1.04, 1.63)). Patients with HIV/syphilis co-infection had lower median CD4⁺ T cell counts and CD4/CD8 ratios at baseline. After initiation of ART, patients co-infected with HIV/syphilis had smaller increases in CD4⁺ T cell counts and CD4/CD8 ratios than patients infected only with HIV. The rate of recurrence of syphilis or reinfection was 9% (n = 128) during seven years of ART.

Conclusion: HIV/syphilis co-infection had a negative impact on immune recovery and antiretroviral effectiveness. RPR titer and HIV viral load should be monitored in patients co-infected with HIV/syphilis, especially in patients with high RPR titers.