sexual and reproductive lives, must represent a priority group for AIDS and STD prevention.
The difference in the age distribution of peak HIV prevalence between men and women occurs in the region because, on average, sexual partnerships are formed between older men and younger women (see also Chapter 2). The distortion of the urban population profile caused by male migration initially resulted in equal numbers of infected men and women (Quinn, 1994). However, male-to-female transmission of the virus is more efficient than female-to-male transmission in the absence of other cofactors (Haverkos and Quinn, 1995), so that as the epidemic has spread into the larger rural population, the absolute number of infections has become higher among women than men (Rowley et al., 1990; Anderson et al., 1991).
One unique feature of the AIDS epidemic in Africa is the remarkable viral heterogeneity of HIV infection. Within HIV-1 there are now nine recognized