Syphilis therapy more likely to fail in patients with HIV

Treatment for syphilis is significantly more likely to fail in HIV-positive individuals that HIV-negative patients, according to research conducted in Baltimore and published in the online edition of Sexually Transmitted Infections. The investigators also found that a large proportion of patients, regardless of their HIV infection status, who were treated for syphilis, did not attend for follow-up to monitor the effectiveness of their therapy.

HIV and syphilis have a complex interaction that is not yet fully understood. Recent outbreaks of syphilis across the industrialised world have disproportionately affected HIV-positive individuals, and there is evidence to suggest that this is due to increased sexual risk-taking amongst this group.

There is also evidence to show that syphilis may facilitate both the transmission and acquisition of HIV infection. HIV has been found in syphilitic ulcers, HIV viral load has been shown to increase during both the primary and secondary stages of syphilis.

Studies have yielded conflicting data regarding the serological response to syphilis therapy in HIV-positive patients, and other studies have shown that HIV-positive individuals appear to be at greater risk of developing neuro-syphilis.

US guidelines recommend the same syphilis therapy for HIV-positive and HIV-negative individuals, but they do stress more aggressive follow-up for patients who are HIV-positive.

Because of continuing questions regarding the efficacy of syphilis therapy in HIV-positive individuals, investigators from Johns Hopkins University in Baltimore, one of the United States' leading providers of HIV treatment and care, designed a retrospective study involving 129 HIV-positive and 168 HIV-negative individuals diagnosed with syphilis between 1992 and 2000. Individuals with primary, secondary and latent syphilis were included in the investigators’ analysis. Response to syphilis therapy was compared between the two patient groups and data were gathered on patient attendance for tests to check the effectiveness of syphilis treatment.

HIV-positive patients were more likely to report five or more recent sexual partners (p < 0.001), have latent syphilis (p < 0.001) and have lower syphilis titres (p < 0.01). HIV-negative patients, however, were more likely to report contact with an individual known to have syphilis (p < 0.001), and have a past history of syphilis infection (p < 0.01).

Treatment for syphilis failed serologically in 29 HIV-positive and seven HIV-negative individuals. However, in seven HIV-positive and two HIV-negative patients this treatment failure was due to reinfection with syphilis.

In multivariate analysis, adjusting for age, past syphilis infection, baseline syphilis titre, type of syphilis therapy, and syphilis stage at diagnosis, the investigators found that the risk of serological failure was higher amongst HIV-positive patients (hazard ratio: 6.0).

The median time to treatment response was 278 days in HIV-positive patients and 128 days in HIV-negative patients, a difference that was statistically significant (p < 0.001). The investigators also found that HIV-positive individuals had a slower response to therapy (median, 342 days), than HIV-negative patients (median, 138 days, p = 0.03).

The investigators' study design included all 3,607 individuals diagnosed with syphilis at Johns Hopkins between 1992 and 2000. However, follow-up data were lacking for 65% of HIV-positive and 77% of HIV-negative individuals and these individuals were excluded from subsequent analysis. “Efforts to ensure more consistent serologic follow-up among patients treated for syphilis, especially those who are infected with HIV, are warranted”, conclude the investigators.