Figure 1. Flow diagram of model.

The model population is divided into females, circumcised males and non-circumcised males. In each group, X₀ is the number of individuals not infected, X₁ is the number with acute HIV infection, X₂ is the number with latent infection, X₃ is the number of people in a stage shortly prior to AIDS and X₄ is the number with AIDS. The rate of progression between these stages of infection is given by σ₁, σ₂ and σ₃ and the rate of death for those with AIDS is σ₄; on average, individuals have acute infection for four months, latent infection for eight years, ‘pre-AIDS’ for twelve months and AIDS for six months. The rate of incidence among females, circumcised and non-circumcised men are represented by λ_f, λ_c and λ_m respectively. The intervention is simulated by moving non-circumcised men into the group of circumcised men, at a rate which can be different for men who are infected from those who are not or different in the different sexual activity groups (not shown): r_s(t).