Table 1.

Epidemiology of HIV-1 discordance among heterosexual African couples

HIV-1 serodiscordance is common
■ Half to two-thirds of HIV-1-infected adults in a cohabitating relationship in Africa have an HIV-1-uninfected partner [6-9]
■ Population-based studies indicate that the HIV-1-uninfected partner in heterosexual serodiscordant couples is equally as likely to be male as female [13]
HIV-1 transmission rates are high
HIV-1 incidence in studies with HIV-1 serodiscordant couples ranges from 2.0 to 11.8/100 person-years (p-y):
■ 2/100 p-y with regular counseling and provision of free condoms [2••, 14]
■ 4/100 p-y for men and 9/100py women in couples VCT cohort study [20]
■ 8.7/100 p-y for men and 9.2/100py for women in a population-based cohort with low condom use [100]
■ 11.8/100 p-y in a retrospective cohort prior to ART scale-up [101, 102]
There are modifiable risk factors for HIV-1 transmission
Plasma viral load	■ High viral load is significantly associated with increased risk of transmission, with 2.3-2.5 increased risk per each log10 increase in plasma viral [27, 101, 103]
ART use by HIV-1 infected partner	■ Early initiation of ART at CD4 350-550 cells/mL reduces risk of transmission to HIV-1-uninfected partners by 96% in context of viral load monitoring, adherence support and risk reduction counseling [14] ■ Observational studies indicate 80-92% reduced HIV-1 transmission in context of ART use by HIV-1-infected partners without virologic monitoring [43-46] ■ In one observational study, equal transmission rate from HIV-1-infected partners on & off ART in context of limited monitoring and adherence counseling [104]
Contraception	■ Effective methods can prevent unintended pregnancies ■ Hormonal contraception associated with two-fold increased risk of HIV-1 acquisition and transmission among HIV-1 serodiscordant couples [76•]; thus, dual condom use and contraceptive options need to be promoted
Pregnancy	■ Pregnancy in the HIV-1-infected or uninfected female associated with two-fold increased risk of male to female and female to male HIV-1 transmission [67•]
Condom use	■ Low condom use among couples, especially among those unaware of their serostatus [4, 7, 20, 23, 100] ■ Condom use is highly protective with 79% lower rate of transmission among HIV-1 serodiscordant couples on a per-act basis [82] ■ Lower infection rates among couples reporting consistent condom use [20, 22, 104] ■ Alcohol use associated with lower condom use [85]
Outside partners	■ Risk from outside partners of unknown HIV-1 serostatus with whom condom use is lower [15] ■ Partners in Prevention HSV/HIV Transmission study: viral linkage indicates 29% of HIV-1 infections in serodiscordant couples were acquired from outside partners [14]. Most outside partnerships reported when the HIV-1-uninfected partner did not report sex with their known HIV-1- infected partner (i.e. were not concurrent) and condom use was lower with outside partners [15] ■ HPTN 052: viral linkage indicates 25% of HIV-1 transmissions from outside partners [2••]
Male circumcision	■ Lack of male circumcision is associated with increased risk of HIV-1 acquisition in men and women [101, 102] ■ Circumcision of HIV-1-uninfected men significantly reduced risk of HIV-1 acquisition [90-92] ■ Observational data indicate circumcised HIV-1 -infected men at lower risk of HIV-1 transmission to their female partners, most of whom were likely to have been circumcised prior to becoming HIV-1-infected [93], but circumcision of HIV-1-infected men did not reduce risk of transmission to female partners in randomized clinical trial [94]