Background: Recent syphilis outbreaks have raised concern regarding the potential enhancement of HIV transmission. The incidence of syphilis and its association with HIV-1 infection rates among a cohort of sexually transmitted infection (STI) clinic attendees was investigated.
Methods: 2732 HIV-1 seronegative patients attending three STI and one gynaecology clinic, were enrolled from 1993–2000 in an ongoing prospective cohort study of acute HIV-1 infection in Pune, India. At screening and quarterly follow up visits, participants underwent HIV-1 risk reduction counselling, risk behaviour assessment and HIV/STI screening that included testing for serological evidence of syphilis by RPR with TPHA confirmation. Patients with genital ulcers were screened with dark field microscopy.
Results: Among 2324 participants who were HIV-1 and RPR seronegative at baseline, 172 participants were found to have clinical or laboratory evidence of syphilis during follow up (5.4 per 100 person years, 95% CI 4.8 to 6.5 per 100 person years). Independent predictors of syphilis acquisition based on a Cox proportional hazards model included age less than 20 years, lack of formal education, earlier calendar year of follow up, and recent HIV-1 infection. Based on a median follow up time of 11 months, the incidence of HIV-1 was 5.8 per 100 person years (95% CI 5.0 to 6.6 per 100 person years). Using a Cox proportional hazards model to adjust for known HIV risk factors, the adjusted hazard ratio of HIV-1 infection associated with incident syphilis was 4.44 (95% CI 2.96 to 6.65; p<0.001).
Conclusions: A high incidence rate of syphilis was observed among STI clinic attendees. The elevated risk of HIV-1 infection that was observed among participants with incident syphilis supports the hypothesis that syphilis enhances the sexual transmission of HIV-1 and highlights the importance of early diagnosis and treatment of syphilis.
- ELISA, enzyme linked immunosorbent assay
- GUD, genital ulcer disease
- MSM, men who have sex with men
- RPR, rapid plasma reagin
- STI, sexually transmitted infections
- TPHA, Treponema pallidum hemaglutination assay
- sexually transmitted infections
- genital ulcer disease
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Funding/support: This work was supported by the Indian Council of Medical Research (ICMR) and by grants from the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH) (AI 41369, AI 01633), through a contract from the NIAID, NIH through Family Health International (FHI) (AI 35173), in part by a fellowship from Fogarty International Center/USNIH (5 D43 Tw00010-AITRP). SJ Reynolds was supported by a grant from the R Samuel McLaughlin Foundation. The views expressed do not necessarily reflect the view of the ICMR, NIH, or FHI.
Previous presentations: Presented in part at the 15th Biennial Congress of the International Society for Sexually Transmitted Diseases Research (ISSTDR), 2003.
Informed consent: Informed consent was obtained from all patients participating in the study. Human experimentation guidelines of the US Department of Health and Human Services and those participating institutions were followed in the conduct of this research.