The HIV/AIDS epidemic. By the end of 1997 more than 30 million adults worldwide were estimated to be infected with HIV, the virus that causes AIDS, a usually fatal condition that has no cure. Of these, about 17 million are men and 12 million are women. The majority of these cases are in the developing world. India has the greatest number of people infected with HIV—more than 4 million (124).

In many developing countries HIV/AIDS is devastating families and communities, striking mostly people in the prime of adulthood. In some sub-Saharan African countries—for example, Burkina Faso and Côte d'Ivoire—AIDS has reduced average life expectancy at birth by more than a decade (286). In Zimbabwe life expectancy is expected to decrease by 25 years by 2010 because of deaths related to AIDS (255).

An estimated 1 million children in developing countries also are infected with HIV or have AIDS. The epidemic is spreading so rapidly and so widely that it jeopardizes many previous gains in child survival, warns Peter Piot, executive director of the Joint United Nations Program on HIV/AIDS (256). Currently, according to the United Nations Children's Fund (UNICEF), about 1,000 children die from AIDS every day. Millions more are left without support when their parents die of AIDS, or they suffer because their parents have AIDS-related diseases, such as tuberculosis, and cannot properly care for their children.

The HIV/AIDS epidemic has put men's sexual behavior in the spotlight (56, 61, 63, 143, 268, 286). Prevention is the only solution. Yet too many men still engage in risky sexual practices, such as having multiple sex partners, including other men, and not using condoms consistently. In some countries, such as Thailand, many married men frequent commercial sex workers and do not use condoms, either with the prostitutes or with their wives (135, 216,243 ). In several Asian and African countries, some older men seek out virgin girls, known as cherry girls, whom they believe to be safe from HIV (42, 234).

Men's sexual behavior puts women at risk. In some countries, including the US and several sub-Saharan African nations, HIV is now spreading faster among women than men (124, 149, 201). In India a study of married and monogamous women at STD clinics found a high rate of HIV and other STDs in this apparently low-risk group (5). The strongest predictor for HIV infection among these women was having a husband who had been diagnosed with an STD.

HIV and other STDs have been described as showing "biological sexism" (107). That is, women are more susceptible physiologically to the viral and bacterial agents that cause them (56, 125, 149). As a result, men transmit infections to women more efficiently than women do to men. For example, men are eight times more likely to transmit HIV to a female partner through repeated, unprotected sexual intercourse than women are to transmit the virus to men (185).

Other STDs. The resurgence in some other STDs also underscores the need for men to practice safe sex. The World Health Organization (WHO) estimates that each year there are more than 330 million cases of curable STDs among adults worldwide (261). This figure includes 89 million new cases of chlamydia infection, 62 million new cases of gonorrhea, and 12 million new cases of syphilis (56). The vast majority of these cases, as with HIV/AIDS cases, occur in the developing world, particularly sub-Saharan Africa.

STDs are more difficult to detect in women, making accurate diagnosis harder (139, 261). Women are less likely than men to receive timely treatment because they may have no symptoms at first, they are embarrassed, or they cannot get to a clinic. As a result, sexually transmitted infections can progress to more serious medical conditions before women seek treatment (56, 139, 261). Thus women suffer more long-term and more painful consequences from STDs, such as ectopic pregnancy, pelvic inflammatory disease, and infertility (125, 261, 280).

Each year an estimated 500,000 women worldwide get cervical cancer (177). It is the leading cancer killer of women in developing countries (186, 245). Cervical cancer is caused by several human papilloma viruses (HPV) that are transmitted through sexual intercourse (50, 175, 177). This type of cancer is entirely preventable and, if caught early, treatable. Early diagnosis, which can be done with a Pap smear of the cervix, can detect the infection at a precancerous stage. Cervical cancer remains a major killer, however, because so few women have access to early diagnosis and treatment (191).

STDs such as gonorrhea and chlamydia can cause infertility in men and women, if left untreated. Often, however, women are blamed for infertility when, in fact, the man may be infertile (16, 56, 72, 287). WHO estimates that 8% to 22% of infertility worldwide is due to male causes (291). Treating men's STDs early and correctly diagnosing fertility problems would help to reduce the social stigma and abuse some women receive when they do not conceive (56).