Table 2.
Model assumptions in terms of key parameter values related to HIV transmission and acquisition in sub-Saharan Africa
| Assumptions | Parameter values | Source |
|---|---|---|
| Probability of acquiring HIV from sources external to the couple per 100 person-years (λ) | Derived from model fits | Derived |
| Probability of acquiring HIV by an individual not in a stable couple per 100 person-years (ϕ) | HIV-population-level incidence rate estimated by SPECTRUM or derived using DHS HIV prevalence | [16, 20] |
| HIV transmission probability per coital act (p) | ||
| Acute infection (p acute) | 0.036 | [22, 25] |
| Latent infection (p latent) | 0.0008 | [22] |
| Average (p) using the Rakai and the Partners in Prevention Studies | 0.00115 | Derived |
| Average (p) using the Rakai Study | 0.0012 | [22] |
| Average (p) using the Partners in Prevention Study | 0.0011 | [23, 24, 26] |
| Frequency of coital acts per month (n) | 8.3 acts per month | [22] |
| Demographic and epidemiological measures | ||
| Number of individuals in reproductive age in the population (N rep_age) | Table 1 | [16] |
| Number of stable sexual couples identified in baseline screening survey (N couples) | Table 1 | [16] |
| Fraction of the population in reproductive age that are engaged in stable couples (f in_couples) | Table 1 | [16] |
| HIV prevalence in the population (P) | Table 1 | [16] |
| Prevalence of stable concordant HIV-negative couples (P SCNC) | Table 1 | [16] |
| Prevalence of stable HIV discordant couples (P SDC) | Table 1 | [16] |
| Fraction of females (index partners) among those initially concordant HIV-negative couples (f indexSCNC) | 50% | Assumption based on Eyawo et al. [27] |
| Fraction of females (index partners) among HIV discordant couples (f indexSDC) | Table 1 | [16] |
| Fraction of circumcised males among concordant HIV-negative couples (f mcpop) | Equal to fraction of circumcised males in the population (Table 1) | [16] |
| Fraction of circumcised males among HIV discordant couples where the female is HIV infected (f mcindex) | Table 1 | [16] |
| Fraction of coital acts protected by condom use (f condom) | Table 1 | [16] |
| Efficacy of condoms in preventing HIV transmission per condom-protected coital act (E condom) | 80% | [24, 28] |
| Efficacy of male circumcision in preventing HIV acquisition among males per coital act (E mc) | 58% | [29–32] |
| Duration | ||
| Between each round of the cross-sectional survey (τ follow-up) | 1 year | Convention for this model |
| Acute infection (τ acute) | 49 days | [25] |
| Latent infection spent by index partner between two subsequent cross-sectional surveys (τ latent) | 134 days | Derived |