You may have heard last month’s news about an aggressive form of HIV that had public health officials in New York scared out of their professional gourds. They isolated the virus from a single man, and reported that it was resistant to anti-HIV drugs and drove its victim into full-blown AIDS in a manner of months, rather than the normal period of a few years. Skeptics wondered whether all the hoopla was necessary or useful. The virus might not turn out to be all that unusual, some said; perhaps the man’s immune system had some peculiar twist that gave the course of his disease such a devastating arc. But everyone did agree that the final judgment would have to