State of our knowledge: the epidemiology of HIV/AIDS.

WHO estimates that more than 14 million adults children and infants have been infected with HIV since the start of the pandemic. Worldwide about 75% of cumulative HIV infections have been acquired through unprotected sexual intercourse especially heterosexual transmission. More than 8 million of these infections are in sub-Saharan Africa but the largest increase in the past year has been in Latin America and South and Southeast Asia each with 1.5 million or more infections. The authors consider the determinants of the heterosexual spread of HIV infection. The baseline efficiency of heterosexual HIV transmission is most likely low. A large survey carried out in the US in 1987 found that only 10% of 772 HIV-infected hemophilic men had transmitted HIV to their regular sex partners after several years of exposure. A sustained and dramatic heterosexual epidemic can therefore only be explained by a common occurrence of transmission co-factors possibly in addition to risk-associated sex behavior patterns. Evidence suggests that the rate of HIV transmission is little dependent upon the frequency of intercourse among discordant couples. This reinforces the idea that as long as a transmission co-factor is not present the risk of HIV transmission remains very low. An advanced stage of disease in the HIV-infected partner however has been confirmed as an important transmission co-factor as is infection with sexually transmitted diseases. There is an increased risk of transmission from men to women especially during anal sex and men have an increased risk of contracting HIV from women if they have sexual intercourse during menses. Consistent condom use between HIV-discordant partners has a significant protective effect against HIV transmission. Lack of circumcision in men the use of vaginal desiccating agents and cervical ectopy are less documented potential cofactors while differences in the infectivity among strains of HIV and markers of cellular immunity observed in HIV-negative people with very high risk behaviors may also play a role. These and other biological and behavioral factors join social factors such as population and individual migration the general prevalence of HIV infection in the community age at first sexual intercourse urbanization and the availability of commercial sex to determine the pattern of the dissemination of HIV infection. These factors should therefore be considered together when designing and implementing interventions. Moreover political commitment must be had to maintain and extend prevention efforts to new areas.