Antiretroviral Therapy Is Associated with Reduced Serologic Failure Rates for Syphilis among HIV-Infected Patients

Background. Syphilis and human immunodeficiency virus (HIV) frequently coexist in patients, but the effects of immunosuppression on the course of syphilis are unknown. Our goal was to determine whether the degree of HIV-mediated immunosuppression and the use of highly active antiretroviral therapy impact syphilis serologic responses. Methods. We assessed all cases of syphilis with positive serologic test results from 1990 through 2006 in a prospective, observational clinical cohort of HIV-infected patients.We defined seroreversion as the loss of reactivity in a patient who previously had a serologic test result positive for syphilis. We defined serologic failure as the lack of a 4-fold decrease in rapid plasma reagin titers 270–365 days after therapy or a 4-fold increase in titers ⩾30 days after therapy. We used Cox proportional hazards models with statistical adjustments for multiple failure instances. Results. One hundred eighty subjects experienced 231 cases of syphilis. The median follow-up time was 5.3 years. A total of 71 episodes of serologic failure were documented. A CD4 cell count of