title: Exposure to infections and risk of leukemia in young children.
abstract: BACKGROUND
  Epidemiologic studies indicate that infections in early childhood may protect against pediatric acute lymphoblastic leukemia (ALL).
  
  
  METHODS
  We identified 3,402 ALL cases among children 0 to 5 years of age using the California Cancer Registry. From California birth records we randomly selected controls in a 20:1 ratio and frequency matched them to cases by birth year. We investigated markers of exposure to infections, including month of birth, timing of birth in relation to influenza and respiratory syncytial virus (RSV) seasons, and birth order based on data from California birth certificates and national infection surveillance systems.
  
  
  RESULTS
  We observed an increased risk of ALL for spring and summer births, and for those first exposed to an influenza or RSV season at nine to twelve months of age compared with those exposed during the first three months of life, and this association was stronger among first born children [odds ratios (OR), 1.44 and 95% confidence intervals (CI), 1.13-1.82, for influenza exposure at nine to twelve months of age]. Decreased risk was observed with increasing birth order among non-Hispanic whites but not Hispanics (OR, 0.76 and 95% CI, 0.59-096, for fourth or higher birth order among whites).
  
  
  CONCLUSIONS
  Our results support the hypothesis that infections in early childhood decrease risk of ALL.
  
  
  CONCLUSIONS
  Our findings implicate early life exposure to infections as protective factors for ALL in young children.
authors.affiliation: Authors' Affiliations: Department of Pediatrics, Division of Epidemiology and Clinical Research, University of Minnesota, Minneapolis, Minnesota; Departments of.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Marcotte
authors.affiliation: Epidemiology and.
authors.forename: Beate
authors.initials: B
authors.lastname: Ritz
authors.affiliation: Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California.
authors.forename: Myles
authors.initials: M
authors.lastname: Cockburn
authors.affiliation: Biostatistics, Fielding School of Public Health, University of California; and.
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.affiliation: Epidemiology and jeheck@ucla.edu.
authors.forename: Julia E
authors.initials: JE
authors.lastname: Heck
mesh_terms: D002675:Child, Preschool; D003141:Communicable Diseases / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000453:epidemiology*; D012307:Risk Factors