PIP:

Although parts of Africa already have a heterosexual epidemic of acquired immunodeficiency syndrome (AIDS), the potential for a major epidemic in the US or Europe remains a subject for speculation. Future heterosexual spread of the human immunodeficiency virus (HIV) is likely to depend on 2 key factors: patterns of sexual and needle sharing behavior; and the probability of transmission of HIV from men to women and from women to men. There is some evidence that the risk of transmission from men to women increases both with the duration of the seuxal relationship and the frequency of sexual contact. Infectivity has been suggested to increase as people progress towards AIDS. The relative risk for transmission by different sexual practices requires further study. Studies of HIV transmission from women to men have been small so that it is difficult to assess the relative risks of transmission from women to men and from men to women. Infectivity of the index case cannot yet be measured. It appears that infectivity varies both between individuals and within individuals over time. Treatment to reduce infectivity may be important in controlling the epidemic.