3.1 The global epidemiological situation
A broad overview of the current epidemiological profile of the HIV pandemic was given by Mr A. Burton, Surveillance, Epidemiology and Forecasting. In the space of just one decade, AIDS has turned into a pandemic affecting millions of men, women and children on all continents. WHO estimates that 4.5 million AIDS cases had occurred by late 1994 and foresees that this cumulative total will triple by the year 2000. The number of people infected with HIV is much greater. According to WHO’S conservative estimates, as of late 1994 more than 18 million adults and over 1.5 million infants had been infected with HIV since the start of the pandemic. By the year 2000, there will be an estimated 30-40 million infections.
A decade ago women were less prominent in the epidemic. The estimated distribution of total adult HIV infections from late 1970s/early 1980s until late 1994 show male/female ratios ranging from 1: 1 in Africa to 6.5: 1 in Australasia, Europe and North America (Table 1). Today, women comprise almost half of all newly infected adults. In 1994 alone, more than one million women have been infected. Already, 7-8 million women have been infected with HIV worldwide and this figure is rapidly growing. Estimates are that over 14 million women will have become infected with HIV by the year 2000, and about four million of them will have died.
Estimated distribution of total adult HIV infections from late 1970s/early 1980s until late 1994, by sex*
* The Current Global Situation of the HIV/AIDS Pandemic; WHO, 3 July 1995 and Women and AIDS-Agenda for action; WHO/GPA/DIR/94.4, 1994
Among both men and women, the hardest-hit group is youth. WHO estimates that half of all infections to date have been in 15-24-year-olds, with a female-to-male ratio of two to one in this age range. An analysis of reported AIDS data from several African and Asian countries suggests that young women under 25 account for nearly 30% of female AIDS cases and young men for approximately 15% of male cases.
The route of transmission to women is overwhelmingly through heterosexual intercourse. In most developing countries, heterosexual transmission has predominated from the outset. In industrialized countries, where homosexual contact and needle-sharing used to account for nearly all infections, there has been a rise in heterosexual transmission. The result is that as local epidemics mature, the net of infection is cast wider. In many countries throughout the world, pregnant women attending antenatal clinics are showing a high prevalence of infection and many of them report having only one partner.
Sexual transmission of HIV accounts for the large majority of new infections (70-80%) and this proportion is increasing. Perinatal infection, blood transfusion and the sharing of injection equipment between injecting drug users (IDUs) account for 5-10% of transmission, each. Transmission in health care settings (e.g. through accidental needle-stick injuries in health care workers) accounts for much less than 1% of infections. Efficacy of transmission also differs by route. Blood transfusion with infected blood will result in transmission to the recipient in nearly 100% of cases (with women receiving more transfusions than men for reasons related to pregnancy and childbirth). The odds are less for those who share drug injecting equipment (25-50%), and mother-to-child transmission (25-30%). It is extremely difficult to calculate the odds of acquiring HIV through sexual intercourse with an infected person: the range of estimates vary from 1/100 per sexual contact to 1/1000.
There is an equally wide disparity between and within countries in terms of the epidemic patterns of heterosexual transmission. In some situations, commercial sex may play an important role in the transmission of HIV, whereas in others, casual sex with multiple partners appears to be more significant. Additionally, many factors come into play such as age of first intercourse, and other sexual behavioural patterns in a given context or country. What is clear and universal, however, is that sexual transmission from male to female is more efficient and frequent than from female to male. WHO estimates that male-to-female transmission may be 2-4 times as efficient as the reverse. The major factors responsible for this are the larger mucosal surface area exposed to the virus in women and the greater viral inoculum present in semen compared with vaginal secretions. Young girls are particularly vulnerable; their immature cervix and relatively low vaginal mucus production presents less of a barrier to HIV.
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