Background: Following syphilis treatment, nontreponemal antibody test titers usually decline and may become nonreactive over time. However, some proportion of patients will fail to achieve nonreactive titers despite an appropriate serological treatment response. We analyzed data from HIV-negative patients with early syphilis to determine seroreversion rates at 12 months after therapy.
Methods: Data were analyzed from a randomized controlled trial of syphilis treatment among HIV-negative patients age >/= 18 with primary, secondary or early latent syphilis conducted in the United States and Madagascar. Rapid plasma reagin (RPR) titers were obtained at 6, 9, and 12 months after treatment. Seroreversion was defined as a negative RPR after therapy. Seroreversions were determined for patients who exhibited >/= four-fold decline in RPR titers at 6 months after therapy. Bivariable analyses were conducted to assess characteristics associated with seroreversion at 12 months after treatment using odds ratios (OR) and 95% confidence intervals (CI).
Results: Of 333 HIV-negative patients with early syphilis who demonstrated an initial serological response, only 17.1% had seroreversion at 12 months after therapy. The proportion of seroreversion was highest at 37.2% (32/86) among those with primary syphilis, and lowest among patients with secondary syphilis at 10.0% (17/170). In bivariable analyses, males had a higher odds for seroreversion (OR 4.4; 95% CI: 2.0-9.6). Primary syphilis patients had a five-fold higher odds for seroreversion (OR 5.1; 95% CI: 2.3-12.7) compared to those with early latent syphilis. Patients with baseline RPR titers </= 1:32 had a high odds for seroreversion (OR of 13.3; 95% CI: 6.5-27.1) compared to those with titers > 1:32.
Conclusions: Despite an appropriate serological response, only 17.1% of HIV-negative patients treated for early syphilis demonstrated RPR seroreversion at 12 months after therapy. Male gender, primary syphilis stage and lower baseline RPR titers were associated with higher odds of seroreversion.