Early child-care and preschool experiences and the risk of childhood acute lymphoblastic leukemia.

An infectious etiology for childhood acute lymphoblastic leukemia (ALL) has been suggested, yet few studies have focused on the role of early child care. Day-care histories were examined in a case-control study of ALL in New York State. Cases (n = 255) were diagnosed at one of four referral centers between 1980 and 1991; controls (n = 760) were randomly selected from livebirths in the 31 counties served by the referral centers. Self-administered questionnaires were mailed to the parents of cases and controls in 1995. Day-care histories were censored at the age of diagnosis for cases and at an equivalent date for controls. The odds ratio for children who stayed at home compared with those who attended day care for >36 months was 1.32 (95% confidence interval (CI): 0.70, 2.52); the odds ratios for 1-18 and 19-36 months of day care were 1.74 (95% CI: 0.89, 3.42) and 1.32 (95% CI: 0.64, 2.71), respectively. Elimination of cases with T-cell ALL enhanced the risk. Starting care at an earlier age was not associated with a decreased risk of ALL. These findings do not support the hypothesis that infrequent contact with peers during early childhood could delay exposure to infectious diseases and increase the risk of ALL.