[Geographical pathology and the working environment (author's transl)].

The geographical, or, more generally, the topographical approach to health and disease has common and important applications in occupational health studies. Analysis of disease occurrence (prevalence and incidence) by area may be carried out at three levels of observation: within the working environment, when different areas usually correspond to different exposures to potentially noxious agents; in the locality where the working environment is situated, which may be affected, for example, by routine industrial discharges or by pollution following accidents; and in the region which includes the locality. Epidemiological tools for the spatial investigation of disease occurrence at each of these levels are reviewed and exemplified, and possible sources of confounding and bias (positive and negative) are emphasized. Attention is particularly drawn to "false negative" results arising in occupational studies because of dilution of an excess risk limited to only some of the workers operating in a defined area.