ABSTRACT
Introduction From the beginning of the epidemic, AIDS exhibited all the classic signs of an infectious disease, and the only convincing explanation for its cause was the emergence of a new infectious agent. An infective aetiology was consistent with the geographical clustering of early cases and epidemiological evidence of case-to-case contact, the newness of the disease, the pattern of groups at risk, its occurrence within the same time scale in the diverse groups affected and, finally, its exponential spread.
