The distribution of early acquired immune deficiency syndrome cases and conditions for the establishment of new epidemics

This article presents discussion on two issues: the distribution of early c ases of acquired immune deficiency syndrome (AIDS), and the epidemiological conditions for the establishment of new diseases. Evidence from four prese ntations on early AIDS cases is discussed, together with issues of interpre ting association and inferring causation. In the second section, the result s of a stochastic epidemiological model using the 'real' geography of villa ges in northern Zaire is presented. This is used to investigate the conditi ons under which newly introduced infections with different characteristics are able to establish in human populations. It highlights additional spatia l, temporal and behavioural conditions necessary for the persistence of int roduced diseases, in addition to the condition that the basic reproductive rate R-0 > 1.