Traffic density and the risk of childhood leukemia in a Los Angeles case-control study.

PURPOSE To investigate the relationship between traffic density and the risk of childhood leukemia. METHODS The study group consisted of 212 cases and 202 controls from the London et al. (1991) study of childhood leukemia conducted in the Los Angeles area during 1978 to 1984. Using GIS methods, traffic counts on all streets within 1500 feet of each subject's residence of longest duration were determined. From these counts, an integrated distance-weighted traffic density measure was calculated for each subject for use as the analytic variable. Additional information, including magnetic fields and wire-code, was obtained from the original case-control study. Association between traffic density and leukemia, and confounding and effect modification by other variables, were assessed using standard matched case-control analyses. RESULTS Although the unadjusted traffic density-childhood leukemia rate ratios were slightly elevated, this weak association was explained by confounding by wire code. Wire code remained associated with leukemia after controlling for traffic density. There was little evidence of effect modification between traffic density and magnetic fields, wire code or other variables. CONCLUSIONS There is no evidence of an association of traffic density with childhood leukemia in the Los Angeles case-control study.