Aids For an epidemic that would explode to claim hundreds of thousands of lives, AIDS surfaced very quietly in the United States, with a small notice on June 4, 1981 in a weekly newsletter published by the Centers for Disease Control in Atlanta, alerting doctors to five unusual cases of pneumonia that had been diagnosed in Los Angeles residents over the previous few months. All the patients were homosexual men who had come down with PCP (Pneumocystis carinii pneumonia), a lung infection usually seen only severely malnourished children or adults undergoing intensive chemotherapy. But until they got sick the California men were well nourished, vigorous adults, whose immune systems should have protected them from the infection. Within the year, similar cases were reported from all over the country: apparently healthy adults who were suddenly getting sick with rare infections and malignancies that healthy people should not get. Most were from New York City, California, Florida and Texas, and not all were homosexual men.

Men and women who used intravenous drugs were also getting sick, as were men with hemophilia, the male and female sexual partners of people in these risk groups, immigrants from Africa and the Caribbean, and some of the infant children born to women at risk. All these varied people had one thing in common: almost absent levels of the white blood cells called T helper cells that keep the immune system functioning properly. Their defective immune systems left them vulnerable to one serious health problem after another. Although many problems could be treated, and even cured, others immediately arose. After their first serious problem, people were said to have AIDS, and once diagnosed with AIDS most survived for only a year or two.

By 1984, the virus called H.I.V. was firmly established as the cause of the mysterious syndrome. H.I.V. can pass from one person to another through sexual contact or contact with infected blood, settle into their T helper cells, and progressively destroy them. A blood test to detect carriers of H.I.V.

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was released in the spring of 1985. For the first time people could be tested to see if they were at risk for developing AIDS, and scientists could get some idea of the form the epidemic, if unchecked, might grow to take in the USA and around the world. The news was not good. The epidemic was shaped like an iceberg, with a small visible tip and a huge invisible base. For every person who was sick with AIDS, thousands of others were infected with H.I.V.

but were still entirely well, and often not even aware that they were infected and able to transmit the virus to others. At the end of 1988, for instance, almost 90,000 Americans had been diagnosed with AIDS, and almost 50,000 had died of the illness, but public health officials were estimating that close to a million might carry the virus. By the peak of the epidemic in 1995, 476,000 Americans had been diagnosed with AIDS, more than half of whom had died. Fortunately, though, the discovery of H.I.V. also let scientists begin to make progress in preventing and treating the disease. For the first time units of donated blood could be tested to make sure they were free from infection before being transfused, and drugs could be tested in the laboratory to see if they could kill the virus and keep the infection from progressing.

The first drug found to have activity against H.I.V. was AZT, which was released for widespread use in 1987. Even used at high doses that came with many side effects, the drug by itelf did not work very well to treat people sick with AIDS, or to prevent healthy H.I.V.-infected people from getting sick. But it did prove to be extremely important in slowing one phase of the epidemic: in 1994 a study showed that AZT was very effective in keeping H.I.V. infection from passing from mother to baby, and numbers of H.I.V. infected newborns began to decline. Meanwhile, other anti-H.I.V.

drugs slowly followed AZT onto drugstore shelves, and doctors began to treat patients with combinations of the most potent ones. In 1996, a set of powerful drugs called the protease inhibitors was released, and the picture of AIDS in the United States began to change. Terminally ill people treated with combinations of protease inhibitors and older drugs — a medication cocktail that often required them to take dozens of pills and capsules a day at precisely timed intervals — suddenly began to regain their health, and the statistics of AIDS in the United States began to change dramatically. In 1996 the death rate from AIDS in the US was 23% less than in 1995, and in 1997 it fell again by more than 40%. The new drug combinations could also stop healthy people who were H.I.V.

infected from getting sick with AIDS, and rates of new AIDS cases began to fall–by 6% in 1996, 15% in 1997, and about 25% in 1998. The new drug combinations have worked so well in some people with AIDS that doctors predict they may survive for years or even decades despite their disease, living normal lives as people do with other chronic treatable conditions like diabetes or high blood pressure. But for many other infected people, the new drugs are only a beginning. H.I.V. is a virus with thousands of different strains and mutations, and it can develop resistance to drugs very quickly. About half the people who initially respond to drug combinations may stop responding because the virus in their bloodstream has grown tolerant to the drugs they are taking. And, more importantly, while the new anti-H.I.V.

treatments have made a big difference in the shape of the AIDS epidemic in the United States and Europe, at $15,000 or more a year they are far too expensive for use in the impoverished countries of Africa and Asia, where the vast majority of the world’s H.I.V. infected people live. For these countries, the best hope against AIDS lies in the development of a vaccine that can prevent people who are exposed to H.I.V. from acquiring the infection. But the same variability that allows H.I.V. to elude drugs also makes it a very difficult to trap the virus into a vaccine.

So the challenges of AIDS research now lie along two lines. First, new drugs must be devised to keep people who are already infected with H.I.V. from getting sick, drugs that are safer and easier to take than the older ones and active against virus that has grown resistant to the older drugs. Second, H.I.V. must be stopped from passing from person to person and causing new infections.

Until an effective vaccine is developed the best methods of preventing new infections seem to be relatively old- fashioned ones: educating people about the disease, encouraging those who may be infected to get tested, and developing effective ways of discouraging illicit drug use and encouraging condom use to prevent sexually transmitted infections. Science.