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 transmission4,10,11.
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 sites1, 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 communities22,
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.