In the early 1990s, heterosexual transmission of the HIV virus became the leading cause of AIDS in women, overtaking the sharing of drug needles. At the beginning of the AIDS epidemic, women and children seemed to be on the periphery. Since the HIV virus entered the heterosexual community (via drug takers, bisexuals and promiscuity), women are now considered at the centre, both of incidence and transmission. The reasons for the transition are many and different for different countries.
Cultural factors set different standards for sexual behaviour for men and women, and expect women to have sexual relations with men who gave them economic support. This combined with adolescent sex means that women are increasingly infected and at a decreasing age. Casual sex and prostitution are also critical factors in some countries. In some African countries, for example, migration often divides families and it is acceptable for a man to take a mistress. Polygamy combined with casual sex also increases dramatically the incidence of infection. Problems typically arise when a young wife of 15 or 16 takes a lover (often older) because her husband cannot satisfy both her and his other wives together. She then infects him and he in turn infects his other wives. Alternatively, he is already a carrier and infects his young wife and the children she bears. In Thailand, casual sex is culturally condoned; estimates of the number of Thai men using prostitutes range between 43% and 97%. One study found that about 50% of married men had had up to five sexual partners other than their wives in the pervious year.
Physiologically women are at a greater risk than men of acquiring HIV from sexual intercourse because HIV is more concentrated in semen than vaginal fluid and is easily absorbed into the vaginal walls. Vaginal secretions become more alkaline on contact with sperm, and as a result the vaginal cells also become more receptive to the virus. Particularly where primary health care is poorer, women who have genital sores and lesions are at much greater risk. Diseases such as syphilis and chancroid greatly facilitate transmission of HIV from both men to women and women to men.
For teenage girls having sexual intercourse, even greater risk arises because the vaginal wall is relatively thin in adolescence. The possibility of damaging friction is higher in women are virgins or who have not had children. Because young people have a higher rate of anal intercourse, there is a similarly higher risk of infection through damage to the thin walls of the rectum. Another factor increasing the vulnerability of young women is the location of the "transition zone" of cells, which lies outside the cervical opening in young women, and that researchers suspect is infected by the HIV virus to cause AIDS (it is also infected by the human papilloma virus which causes cervical cancer); as women mature, the zone moves to a less exposed position inside the uterine opening). Finally young girls are more at risk than boys of similar age because they often have sex with older, more experienced, men, who are more likely to be infected than boys.
For an HIV epidemic to take off in a country's general population, there also has to be a substantial amount of sexual mixing among adults. To sustain a heterosexual epidemic, on average each infected person must have unprotected sex with a minimum of two partners, becoming infected by one and passing on the infection to at least one other. Indeed, since not every encounter between an HIV-positive and an HIV-negative partner will result in a new infection, a sustained heterosexual epidemic suggests that a substantial proportion of the population, both male and female, have a number of sex partners over their lifetimes.
According to WHO, AIDS in the 1990s is transmitted to 60% by vaginal intercourse, 15% by anal intercourse, 10% by infection during drug abuse, 10% as perinatal infection (mother to baby), 5% by blood transfer and 1% in other ways. By 2000, it is projected that over 80% of all HIV infections will result from heterosexual intercourse, although this varies between countries. In the UK in 1993, the proportion of heterosexually-caused infections was believed to be around one-quarter of the total. 73% were probably exposed abroad and 13% had a high-risk partner, but there is a small but growing number of people (117, or 5%, of a total of 2,237 cases reported between 1982 and 1992) who have become infected by partners in the "no-risk" categories. The projected incidences of AIDS in the UK in the year 1997 are 770 among heterosexuals compared with 1,350 cases among gay men and 165 cases among injecting drug users.
A Thai survey in 1992 showed that 60% of women thought they were not at risk from HIV/AIDS, even though 42% suspected their husbands of using prostitutes. Only 2% thought they could infect their baby while 17% thought that they could catch AIDS from the toilet. According to the UK Health Education Authority, while 23% of women said they had changed their behaviour because of AIDS, only 5% had done so by using condoms (the other 17% by adjusting their choice or number of partners). Many woman say they are reluctant to suggest condoms because it might bring an element of distrust into the relationship or deflate a man's ego, and others are reluctant to carry condoms because they might be thought of as a "tart". Ironically, many teenage girls abandon condoms as soon as they get the Pill, as women still regard the risk of pregnancy as their primary concern.
Since the gathering of statistics about AIDS began in the UK in 1982, a total of 8,001 cases have been reported, of which 595 are female. However, in the two years ending August 1993, while the number of male cases increased only 6%, the rise for women was 32%. In 1992 in the USA, women accounted for just 14% of AIDS cases, but the rate climbed 9.8% during the 12 months compared with 2.5% for men. In nine leading cities in the USA, AIDS was the leading cause of death for women of childbearing age in 1992, and is the leading cause of death of women between the ages of 25 and 35 in New York City (where it is also for men of the same age group).
In most of the Third World, where AIDS is overwhelmingly a heterosexually transmitted disease, there are as many female cases as male and sometimes more. At an ante-natal clinic in Rwanda, a quarter of women with only one lifetime sexual partner had been infected with HIV. According to WHO, the number of prostitutes in Bombay's red light districts (total 100,000) who tested positive for HIV rose from 1% in 1987 to 35% in 1992. The Public Health Ministry of Thailand estimates that six percent of the country's 650,000 prostitutes are infected with HIV, although this is considered a gross underestimate. In 1995, it is predicted that the HIV incidence for Thai men and women will be equal, whereas in 1986 there were 17 male cases for every one female. In Uganda there are five times more AIDS cases in young women between the ages of 15 and 19 than among young men of the same age. A study of 210 adolescent girls found that 70% had had sex before the age of 14 -- in many cases with men up to 20 years older. An estimated 140,000 Tanzanian teenagers were HIV positive in 1993. The total is expected to double within two years. Half the teenage girls in a New York clinic who were HIV-positive had had fewer than five sexual partners. Women between the ages of 15 and 25 make up about 70% of the 3,000 women a day who become infected with the AIDS virus and of the 500 women a day who die of AIDS. More than 3 million women were infected in 1991. More than 1 million women will have been infected in 1993, and by the year 2000 the number of affected women will total over 13 million, about 4 million of who will have died.