into their T helper cells, and progressively destroy them. A blood test to detect carriers of H.I.V. 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...
