Modeling the population-level effects of male circumcision as an HIV-preventive measure: a gendered perspective

Abstract

Background: Evidence from biological, epidemiological, and controlled intervention studies has demonstrated that male circumcision (MC) protects males from HIV infection, and MC is now advocated as a public-health intervention against HIV. MC provides direct protection only to men, but is expected to provide indirect protection to women at risk of acquiring HIV from heterosexual transmission. How such indirect protection interacts with the possibility that MC campaigns will lead to behavior changes, however, is not yet well understood. Our objective here is to investigate the link between individual-level effects of MC campaigns and long-term population-level outcomes resulting from disease dynamics, looking at both genders separately, over a broad range of parameters.

Methods and findings: We use simple mathematical models of heterosexual transmission to investigate the potential effects of a circumcision scale-up, combined with possible associated behavioral disinhibition. We examine patterns in expected long-term prevalence using a simple equilibrium model based on transmission factors, and validate our results with ODE-based simulations, focusing on the link between effects on females and those on males.We find that the long-term population-level effects on females and males are not strongly linked: there are many possible ways in which an intervention which reduces prevalence in males might nonetheless increase prevalence in females.

Conclusions: Since an intervention that reduces long-term male prevalence could nonetheless increase long-term female prevalence, MC campaigns should explicitly consider both the short-term and long-term effects of MC interventions on females. Our findings strongly underline the importance of pairing MC programs with education, support programs and HIV testing and counseling, together with other prevention measures.

Figure 1. Simplified model diagram.

Disease is transmitted among females, and circumcised and uncircumcised males (indexed by , and . Susceptible individuals () exposed to infection move to infectious classes ). represents “births” (really, recruitment to sexual activity) in males and females respectively. is the rate at which males become circumcised; it is calculated to give the desired equilibrium proportion of circumcised susceptible males. The forces of infection are given by , , , , where is prevalence in each class, s are intrinsic transmission rates, and is the heterogeneity parameter. represents direct protection of circumcised males, and represents disinhibition. Our ODE model has four identical sub-boxes for each infectious box, to better match the time distribution of the infectious period .

Figure 2. Expected population-level equilibrium prevalence as a function of individual-level “transmission factors”.

Contours for women's (men's) prevalence are shown in red (blue). The shapes show the pre-intervention equilibrium (solid circle), and possible long-term effects of an intervention which results in direct protection for men without (square) and with (triangle) an increase in risky behavior due to disinhibition. The heterogeneity parameter is . The shaded area shows the region in which equilibrium prevalence in women increases while that in men decreases.Other combinations of parameters, and parameter changes,, and parameter changes, can be evaluated in a similar fashion, by comparison with the red and blue lines.

Figure 3. HIV prevalence response to a circumcision intervention.

Curves show prevalence through time in females (red) and males (blue) in a hypothetical population with (dashed lines) and without (solid lines) the introduction of circumcision in year 2010. We assume that circumcision does not change behavior.

Figure 4. HIV prevalence response to a circumcision intervention with behavioral disinhibition.

Curves show prevalence through time in females (red) and males (blue) in a hypothetical population with (dashed lines) and without (solid lines) the introduction of circumcision in year 2010. We assume that behavioral disinhibition leads to a 50% increase in effective transmission for interactions involving circumcised males. Dotted lines show the case where disinhibition does not occur among individuals who were HIV-positive at the time of circumcision (see text).