A prospective study of the influence of HIV status on the seroreversion of serological tests for syphilis

Abstract

The evolution of serological tests for syphilis (STSs) after therapy in HIV+ patients is a major point of controversy, with possible seroreactivation and illicit seroreversion in these patients. The aim of our study was to evaluate the long-term outcome of STSs in a cohort of HIV+ male homosexuals with a history of treated syphilis as compared with HIV- controls.

Patients and methods: Sixty-nine HIV+ male homosexuals with a documented history of treated syphilis and positive baseline treponemal tests were prospectively studied between 1986 and 1993. A medical examination, HIV staging, CD4+ cell count, VDRL, FTA-Abs tests and TPHA were performed every 6 months. Controls consisted of 49 HIV- patients with similar inclusion criteria over the same period. Comparisons between subgroups were based on chi(2) and Kruskal-Wallis tests. Analysis of negativation of the STS used the failure data methods (Kaplan-Meier, log-rank and Cox's model).

Results: Patients had a mean age of 38 years, a baseline CD4+ cell count of 578/mm(3), elapsed time since last syphilis of 7.5 years and a median follow-up of 4.3 years. Controls had a mean age of 42 years, elapsed time since last syphilis of 5.3 years and a median follow-up of 4.7 years. Time to seroreversion was shorter in HIV+ patients for TPHA (p = 0.009, log-rank test) and FTA-Abs test (p = 0.001, log-rank test), even after adjustment for stage of syphilis, age and time since the last episode of syphilis. The decrease in VDRL titres was not different between the 2 groups (p = 0.053, log-rank test). Seroreversion of the TPHA, FTA-Abs test and VDRL test was not significantly related to stage of syphilis, time elapsed since the last episode of syphilis, age or history of STDs in both groups. Seroreversion of the TPHA and VDRL test was not related to baseline CD4+ cell count. However, seroreversion of the FTA-Abs test was related to a low baseline CD4+ cell count (p = 0. 003). In HIV+ patients, a significant decrease in titres was noticed for TPHA, FTA-Abs test and VDRL test over time, but this time effect remained only for TPHA titres after adjustment for the CD4+ cell count.

Conclusion: TPHA may serorevert in HIV+ patients. Thus, a non-reactive TPHA does not exclude a past syphilis infection in such patients. Evolution of the VDRL test after therapy is regular in HIV+ patients. The VDRL test remains adequate for controlling the efficacy of treatment in these patients.