Spatial clustering of Hodgkin's disease in the San Francisco Bay area

Numerous investigations of time-space clustering in Hodgkin's disease, designed to investigate its communicability, have produced equivocal results. Few studies have considered the spatial clustering reflecting a broader range of exposures despite sporadic evidence of such groupings of Hodgkin's disease cases. This project examined spatial (residential) patterns among 741 white Hodgkin's disease cases from the San Francisco-Oakland, California, area using 1969-1977 cancer registry incidence data and 1970 population counts. Two types of distances between cases were evaluated using new statistical methods that adjust for population density. Hodgkin's disease cases lived closer to their nearest case neighbors than expected in four of five study counties. Significant clustering of this type occurred among case subgroups defined by sex, age, and social class. There was little evidence of larger-scale clustering around a single point-source exposure. The small, widely dispersed clusters detected here suggest late exposure to a ubiquitous environmental agent involved in Hodgkin's disease etiology. These case aggregations are consistent both with prior reports of spatial clustering in this lymphoma and with evidence implicating viral or other factors in its pathogenesis.