Predictors of serofast state after treatment for early syphilis in HIV-infected patients

Non-treponemal serological tests are used to monitor treatment response during syphilis infection. Syphilis- and HIV-coinfected patients may experience incomplete resolution in non-treponemal titres, which is referred to as the serofast state. The goal of this study was to evaluate risk factors for serofast state in HIV-infected patients.

From November 2015 to June 2018, 1530 HIV-positive patients were tested for syphilis using a Treponema pallidum particle agglutination (TPPA) assay. Among TPPA-positive patients, medical records were reviewed for early syphilis infection. Serofast state was defined as a less than four-fold decrease in non-treponemal antibody titres during a 6-month follow-up period in the absence of symptoms of syphilis. Baseline characteristics were tested as predictive factors of serological response.

In all, 515 patients (33.7%) tested positive in TPPA assays, and in 163 patients at least one previous syphilis infection was documented. A total of 61 out of 163 patients (37.4%) were in a serofast state. A history of previous syphilis infection (61 vs. 43%; P = 0.04) was more common in serofast patients than in patients with serological cure after 6 months. Non-treponemal titres ≥ 1:32 before therapy (47 vs. 25%; P = 0.005) and adjunctive corticosteroids to prevent the Jarisch-Herxheimer reaction (35% vs 15%; P = 0.006) were associated with serological cure after 6 months, but corticosteroid therapy had no influence at 12 months. The intensity of syphilis treatment did not affect serological cure.

Corticosteroids for prevention of the Jarisch-Herxheimer reaction were associated with earlier serological cure. Although serological response is the accredited surrogate method to monitor syphilis treatment, the biological significance of the serofast state remains unclear.