Hopkins and colleagues examined response to syphilis therapy among 256 patients in Ireland; they reported 15.5% loss to follow-up and 22% "treatment failure."
The only method available to "prove" cure of syphilis depends on a 4-fold (2-dilution) reduction in the antibody response to a nontreponemal antigen (Venereal Disease Research Laboratory [VDRL], rapid plasma regain [RPR]). Failure of therapy or reinfection is suggested by stable or rising antibody titers; such patients are often re-treated. Repeat serologic testing and clinical exam in HIV-negative (normal hosts) persons are recommended 6 and 12 months after therapy. Use of the serologic response to prove cure is less than ideal because (1) host responses are highly variable; (2) failure and reinfection cannot be discriminated; (3) tests between labs may vary considerably; and (4) most tests are not done with paired serum, allowing variation within a lab. However, no other test for proof of cure of syphilis is available. With these criteria, a 20% failure rate is common, depending on the stage of syphilis disease being treated.
Patients with HIV infection receive the same treatment as HIV-negative patients. However, differences in baseline serologic response include high-antibody titer or, less commonly, absent antibody response. Hopkins and coworkers noted no significant difference in response to therapy in HIV-infected patients; however, treatment failure was apparently less commonly observed in HIV-infected patients receiving antiretroviral therapy. Because of increased concern about treatment failure in HIV-infected patients, the CDC Sexually Transmitted Disease Advisory Panel recommends more frequent serologic testing and clinical exam in HIV-infected subjects (eg, every 3 months for 1 year in primary syphilis), with repeat follow-up at 2 years for all such patients.