An ecologic study of childhood leukemia and population mixing in Ontario, Canada

Abstract

Objective: To examine the association between population mixing and the incidence of childhood leukemia, specifically the acute lymphocytic leukemia (ALL) subtype among young children.

Methods: This ecologic study was based on incidence rates of leukemia in children aged 0-14 years. The Ontario Cancer Registry was used to identify the residence of 1394 leukemia cases between 1978 and 1992. Ecologic units were composed of census subdivisions in a 5-year period. Percent population change, determined from the Census of Canada, was employed as a measure of population mixing. The relationship between population mixing and childhood leukemia was examined separately after stratifying by the level of geographic isolation, defined according to urban-rural status. Analyses were also conducted separately in specific age groups and for the ALL subtype.

Results: Population growth in rural areas was associated with an increased incidence of leukemia, particularly for the ALL subtype in children aged 0-4 years (rate ratio = 1.8, 95% confidence interval 1.1-2.8, for a greater than 20% population change relative to no increase in population). In contrast, an elevated risk due to population mixing was not observed in urban areas.

Conclusions: Results from this study are consistent with results from similar studies conducted in the United Kingdom, which are suggestive of a role for an infectious agent in the etiology of childhood leukemia, as proposed in the Kinlen hypothesis.