This paper contrasts biomedical and epidemiological approaches to the diagnosis and treatment of disease, and uses Collingwoods principle of the relativity of causes to show how different approaches focus on different causal factors reflecting different interests. By distinguishing between the etiology of a disease and an epidemic, the paper argues that, from an epidemiological perspective, poverty is an important causal factor in the African AIDS epidemic and that emphasizing this should not be considered incompatible with recognizing the causal necessity of (...) HIV for the AIDS disease. (shrink)