HIV infection is most commonly due to unprotected sex with an infected partner, but can also occur from receiving contaminated blood, or exposure to non-sterile instruments or medical procedures (Buve et al., 2002). As most infected children under 15 years have contracted the virus by transmission from their mothers, their number reflects the prevalence of the infection in women of childbearing age.
In Africa, HIV prevalence varies considerably. In most countries in Southern Africa more than one in five pregnant women are HIV-infected, and in a few sub-Saharan countries median HIV prevalence in antenatal clinics in 2003 exceeded 10%. In some urban settings in Southern Africa antenatal sero-prevalence reaches over 40% (Buve et al., 2002: UNAIDS, 2002). "Across most of sub-Saharan Africa, including parts of Southern Africa, HIV prevalence among pregnant women visiting antenatal clinics has been roughly level for several years - albeit at very high levels in Southern Africa." (UNAIDS,
2002). It should be noted that the apparent stabilization of prevalence rates observed in most of sub-Saharan Africa is due to the matching of the persistently high number of annual new HIV infections with the equally high number of AIDS deaths.
In West Africa HIV prevalence in pregnant women remains generally stable at low levels, though in some urban areas it exceeds 10%; in rural areas the rates are generally lower. In East Africa and parts of Central Africa prevalence among pregnant women has fallen sharply from its high levels of a decade ago. In Addis Ababa, for instance, among 15-24-year-old pregnant women, prevalence has fallen to about 11% in 2003 from around 24% in 1995 (WHO/UNAIDS,
Asia is experiencing a rapidly growing epidemic: seroprevalence rates in some cities or provinces of Indonesia, Cambodia, India and Thailand range from 1% to 5% (UNAIDS/WHO, 2002). Eastern Europe similarly is seeing an exceptionally rapid increase in prevalence, especially among injecting drug users; almost 80% of new infections occur before the age of 29 years. Women account for an increasing share of newly diagnosed HIV infections - 33% in 2002 com pared with 24% a year earlier. One consequence is a sharp rise in mother-to-child transmission. In six countries in the Caribbean Basin the most recent national estimates have shown HIV prevalence among pregnant women reaching or exceeding 2%. In Central and South America, HIV-1 prevalence rates among pregnant women range from 0.1% to 5.0% (WHO/ UNAIDS, 2003).
The risk of mother-to-child transmission is increased if a breastfeeding mother is newly infected, owing to the initially high levels of virus. Preliminary evidence from a study in Zimbabwe suggests that about 4% of women who were HIV-negative when giving birth become infected in the first year postpar-tum, and that the risk continues into the second year (J. Humphrey, personal communication, 2002). This merits attention as in this population 85% of women still breastfeed at 15 months and 30% at 21 months. Similar findings have been reported from another study in Zimbabwe, with 66 new infections among 372 women, nearly 5%, over the two years postpartum (Mbizvo et al., 2001). HIV- prevention interventions directed at pregnant and lactating women could contribute greatly to reducing mother-to-child transmission, but this possibility has so far attracted little research or programmatic effort.
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