The seasonal risk of pediatric/juvenile acute lymphocytic leukemia in the United States.

Acute lymphocytic leukemia (ALL) occurring in pediatric and juvenile patients of nine U.S.A. locations during 1973 through 1980 was investigated by epidemiologic methodology. Time series periodic regression analysis of the monthly cumulative risk for ages 0-19 years revealed evidence of trimodal periodicity at seven of the nine locations tested. Combined analyses revealed a significant effect of latitude in causing asynchrony of the trimodal patterns observed. The average risk maxima occurred in April, August, and December for U.S.A. locations with latitude above 40 degrees (Seattle, Nebraska, Iowa, Detroit, and Connecticut), and in February, July, and October for other locations (San Francisco, Utah, New Mexico, and Atlanta). Because periodic regression analysis is a complex method, independent validation tests were performed to supplement the original results. Here, the best symmetric trimodal sine curve model of each location was utilized to predict the average pattern among the remaining locations of similar latitude. These validation tests supported the existence of similar trimodal patterns for all of the southern locations, and all of the northern locations except Connecticut. The observed peaks in monthly ALL risk coincide with seasonal elevations in the rates of allergenic and infectious diseases, elements of which are capable of promoting lymphocytic proliferation and transformation. Annual disease rates were significantly lower in populations with a high proportion of Blacks or American Indians compared to predominantly Caucasian populations. The possibility that seasonal factors (environmental allergens and/or infectious agents) promote leukomogenesis via indirect mechanisms is briefly discussed.