The 14th-century Black Death killed one-third of Europe's population, but it was in the air, food and water, so breathing, eating and drinking were risky behaviors. AIDS is much more difficult to acquire. Like other large components of America's health care costs (e.g., violence, vehicular accidents, coronary artery disease, lung cancer), AIDS is mostly the result of behavior that is by now widely known to be risky.
The U.S. epidemic, which so far has killed 530,000, could have been greatly contained by intense campaigns to modify sexual and drug-use behavior in 25 to 30 neighborhoods from New York and Miami to San Francisco. But early in the American epidemic, political values impeded public health requirements. Unhelpful messages were sent by slogans designed to democratize the disease -- ``AIDS does not discriminate'' and ``AIDS is an equal opportunity disease.''
By 1987, when President Reagan gave his first speech on the subject, 20,798 Americans had died, and his speech, not surprisingly, did not mention any connection to the gay community. No president considers it part of his job description to tell the country that the human rectum, with its delicate and absorptive lining, makes anal-receptive sexual intercourse dangerous when HIV is prevalent.
Twenty years ago a San Francisco public health official explained death's teaching power: Watching a friend die, like seeing a wreck along a highway, is sobering. But after driving more slowly for a few miles, we again speed up. AIDS has a more lasting deterrent effect.
There has, however, been an increase in unsafe sex because pharmacological progress has complicated the campaign against this behavior-driven epidemic. Life-extending cocktails of antiviral drugs now lead some at-risk people to regard HIV infection as a manageable chronic disease, and hence to engage in risky behavior. Furthermore, the decline of AIDS mortality means that more persons are surviving with HIV infection -- persons who can spread the virus. And drugs like Viagra mean that more older men are sexually active.
Still, even with no pharmacological silver bullet, AIDS deaths in America have been declining for a decade. In Africa, where heterosexual sex is the primary means of transmission, the death rate is steady relative to population growth, and the age of beginning sexual activity is rising, as is the use of condoms. Human beings do learn. But they often do at a lethally slow pace.