(Caldwell and Caldwell, 1993). By contrast, rural women's labor force participation in East Africa has largely been confined to subsistence farming and beer-making. In urban areas in East Africa, women are engaged mainly in the preparation and sale of food products or the production of alcoholic beverages, the latter being closely linked to the commercial sex industry (Caldwell and Caldwell, 1993). Finally, divorced or separated women in East Africa are less likely to retain their children or to be able to return to their families of origin. Therefore they are more likely, the Caldwells argue, to be forced to turn to prostitution (Caldwell and Caldwell, 1993).
Knowledge of social and sexual networks, and of their determinants, is important in projecting the future course of the epidemic and in developing preventive strategies. Studies have begun to address how sexual and social networks channel and potentially amplify HIV transmission in sub-Saharan Africa (Dyson, 1992; Caldwell et al., 1993; Orubuloye et al., 1994; Morris et al., 1995); in addition to migration and transportation systems, such networking encompasses the role of local markets (Edmondson et al., 1993; Orubuloye et al., 1993) and local "mating networks" (Orubuloye et al., 1991; Caldwell et al., 1992; Obbo, 1993). Asymmetric age matching, whereby young women have sexual contact with older men, results in a young cohort of women being exposed to older male partners with higher HIV prevalence (Edmondson et al., 1993; Ssengonzi et al., 1995); this pattern facilitates the spread of infection from generation to generation. Perhaps even more significant, the social context of marriage and childbearing is changing dramatically (Bledsoe and Cohen, 1993). Until recent decades, females in most African societies married at puberty, and there were strong religious sanctions against sex before circumcision or nubility or pubertal ceremonies. Now, according to some evidence, age at menarche may be declining, and formal education and other forms of training are delaying marriage. The result is an ever-rising number of postpubertal single women as a feature of society (see, for example, Antoine and Nanitelamio, 1991).
The composition of sexual networks may have strong implications for the speed or direction of viral transmission. Patterns observed in some African settings of mixing between people in high-risk core groups and others in the general population (as opposed to simple assortative mixing with strong within-group partner preference, such as pairings confined to well-defined groups) can result in substantial spread of sexually transmitted infections, including HIV, among the general population (see Anderson and May, 1992). There is also a growing realization that outside partnerships concurrent with a recognized union, including those that are stable and long term (a not uncommon phenomenon in many sub-Saharan African settings), may be frequent sources of HIV transmission—potentially