The epidemiology of AIDS.

In a remarkably short time researchers have elucidated the basic molecular sequence and structure of the HIV virus that causes AIDS. But we still lack knowledge about many of the biological and social factors that govern transmission of HIV infection at the population level so that long-term predictions about the future of AIDS epidemics in developed and developing countries are very uncertain. It is rather as if we had determined the molecular sequences in human DNA yet did not know how many children the average woman was capable of producing over her lifetime. Specifically one important uncertainty concerns the probability that HIV infection will be transmitted from an infected individual to a susceptible partner over the duration of their relationship. We know little about the transmission probabilities in sexual relations (whether between homosexual males from males to females or from females to males) between needle-sharing drug users or from mother to fetus. (excerpt)