Miasma and "social factors" in disease causality: lessons from the nineteenth century.

Conventional public health wisdom holds that the end of the nineteenth century saw a dramatic change in beliefs about what causes disease, as early convictions about the importance of broad social factors gave way to a concentration on microorganisms. I argue, however, that in both the middle and late nineteenth century nearly everyone, professionals and laypeople alike, saw disease causality in terms of precise, invisible entities, and that prevention policies were as reductionist and narrow as the available technology would allow. My argument is based on a rereading of the primary documents that other scholars have seen as supporting the idea of two distinct public health periods, and on a new interpretation of the revisionist history that questions the idea. I suggest that health policy analysts today are too vague about the meaning of "social factors" and that disease prevention policies might be better if the term was clarified.