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Epidemiology of HIV

HIV is transmitted in only three ways: through unprotected sexual intercourse, heterosexual or homosexual; through blood or blood products, donated semen or organs; or from an infected mother to her child (vertical or mother-to-child transmission). More than 70% of infections are a result of heterosexual transmission and over 90% of infections in children result from mother-to-child transmission^4,10,11.

Although the HIV epidemic is centred in the developing world, AIDS has also become a leading cause of death for young women in the United States of America (USA)^12,13,14. In developed countries, HIV seropositive women are more likely to be intravenous drug users, partners of drug users or bisexual men, or be involved in sex work ^15,16,17. In one American study, 47% of mothers of HIV-infected infants were intravenous drug users, and 22% reported sex with an intravenous drug user¹⁸.

The situation is very different in developing countries, where heterosexual transmission is the predominant mode of spread. Southern Africa is the most affected region¹. In Kenya, Malawi, Namibia, Rwanda, South Africa, the United Republic of Tanzania, Zambia and Zimbabwe, over 10% of women attending antenatal clinics in urban areas are HIV-positive, with rates of almost 60% in some sites^{1, 10, 19, 20, 21} . To date, Africa has been the centre of the epidemic but a rapid rise in infection rates has been seen in south-east Asia. In Thailand, prevalence in women in antenatal clinics has climbed from 0% in 1989 to 2.3% in 1995 and continues to rise. Similar increases are reported from some Indian cities, Latin America and the Caribbean¹⁰. While prevalence rates in antenatal women have been taken as a good indication of the rate of infection in communities^{22, 23} sentinel surveillance at antenatal clinics may underestimate the population prevalence, as shown in a study in the Mwanza district of the United Republic of Tanzania, where the prevalence in antenatal attenders was below that of the general population by a factor of 0.75²⁴. A decrease in the fertility of HIV-infected women, both from subfertility and from increased early pregnancy loss, as reported from the Rakai district in Uganda, may exacerbate this underestimation²⁵.

In urban Uganda there has been a reported decrease in the prevalence of HIV infections in pregnant women over the past few years. The 20% drop in prevalence is thought to be due to behaviour change following aggressive AIDS education campaigns²⁶.