Steven Epstein / University of California Press, $29.95, pp 465 / ISBN 0 520 20233 3 Just 20 years ago it was all simple. With the global eradication of smallpox, the scourge of infectious disease seemed finally defeated. Drug companies had developed production line techniques of drug innovation, and the routine use of randomised, double blind trials would ensure that tragedies like thalidomide would be a thing of the past. Research scientists would develop cures, doctors prescribe them, and grateful patients swallow them; the expert was in his heaven, the public was in its place, and all was right with the medical world. The main reason why that “golden age” of the 1970s now seems so far away is AIDS. The lethal new disease that broke up the party is still–a decade and a half and a billion dollars later–without vaccine or cure and is spreading globally out of …