Objectives: A synergy between HIV and herpes simplex virus type 2 (HSV-2) infections has been reported in observational studies. The objectives of this study were to estimate the per-sex-act female-to-male transmission probabilities (FtoMTPs) of HIV and HSV-2, the effect of each infection on the FtoMTP of the other and the effect of male circumcision on these FtoMTPs.
Design: We used longitudinal data collected during the male circumcision trial conducted in Orange Farm (South Africa).
Methods: Results were obtained by specific mathematical modeling of HIV and HSV-2 statuses of the men as functions of their sexual behavior and male circumcision status. The model took into account an estimation of the HIV and HSV-2 statuses of each of their female partners. Confidence intervals (CI) were estimated using a bootstrap re-sampling method.
Results: The HIV and HSV-2 FtoMTPs, during an unprotected sexual contact for an uncircumcised male in the absence of the other virus in both partners, were 0.0047 (95% CI: 0.0014–0.017) and 0.0067 (95% CI: 0.0028–0.014), respectively. HSV-2 in either partner increased HIV FtoMTP with a relative risk (RR) of 3.0 (95% CI: 1.01–7.3). Conversely, HIV in either partner increased HSV-2 FtoMTP (RR = 2.5; 95% CI: 1.1–6.3). Male circumcision significantly decreased these probabilities with RRs of 0.24 (95% CI: 0.11–0.44) and 0.59 (95% CI: 0.36–0.91), respectively.
Conclusion: This study gave the first estimates of HSV-2 per-sex-act FtoMTPs in Africa. It demonstrated a synergy between HIV and HSV-2 infections and a protective effect of male circumcision on HSV-2 acquisition by males.