This comment on 'Wellings K, Collumbien M, Slaymaker E, et al. Sexual behaviour in context: a global perspective. Lancet 2006; 368: 1706-1728' agrees that the distinction between serial and concurrent partnerships is crucial and that longer term concurrent partnerships seem to be particularly common in some African countries. It also suggests another explanation for Africa's high HIV rates. Many studies have shown that the poorest Africans—especially subsistence farmers—tend to have lower HIV infection rates than traders, businessmen, and other relatively wealthy people. In Africa, many longer term relationships that do not involve prostitution nevertheless tend to have a powerful \"transactional\" element. People with more disposable income might thus be more able to maintain multiple, concurrent relationships.
The Lancet 369 (9561) p.557 [doi:10.1016/S0140-6736(07)60269-4]