title: Population mixing and the risk of childhood leukaemia in Switzerland: a census-based cohort study.
abstract: Childhood leukaemia (CL) may have an infectious cause and population mixing may therefore increase the risk of CL. We aimed to determine whether CL was associated with population mixing in Switzerland. We followed children aged <16 years in the Swiss National Cohort 1990-2008 and linked CL cases from the Swiss Childhood Cancer Registry to the cohort. We calculated adjusted hazard ratios (HRs) for all CL, CL at age <5 years and acute lymphoblastic leukaemia (ALL) for three measures of population mixing (population growth, in-migration and diversity of origin), stratified by degree of urbanisation. Measures of population mixing were calculated for all municipalities for the 5-year period preceding the 1990 and 2000 censuses. Analyses were based on 2,128,012 children of whom 536 developed CL. HRs comparing highest with lowest quintile of population growth were 1.11 [95 % confidence interval (CI) 0.65-1.89] in rural and 0.59 (95 % CI 0.43-0.81) in urban municipalities (interaction: p = 0.271). Results were similar for ALL and for CL at age <5 years. For level of in-migration there was evidence of a negative association with ALL. HRs comparing highest with lowest quintile were 0.60 (95 % CI 0.41-0.87) in urban and 0.61 (95 % CI 0.30-1.21) in rural settings. There was little evidence of an association with diversity of origin. This nationwide cohort study of the association between CL and population growth, in-migration and diversity of origin provides little support for the population mixing hypothesis.
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012, Bern, Switzerland.
authors.forename: Judith E
authors.initials: JE
authors.lastname: Lupatsch
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012, Bern, Switzerland.
authors.forename: Claudia E
authors.initials: CE
authors.lastname: Kuehni
authors.affiliation: University Children's Hospital Zurich, Steinwiesstrasse 75, 8032, Zurich, Switzerland.
authors.forename: Felix
authors.initials: F
authors.lastname: Niggli
authors.affiliation: Department of Paediatrics, University of Bern, Freiburgstrasse 4, 3010, Bern, Switzerland.
authors.forename: Roland A
authors.initials: RA
authors.lastname: Ammann
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012, Bern, Switzerland.|Centre for Infectious Disease Epidemiology and Research, University of Cape Town, Rondebosch, Cape Town, 7700, South Africa.
authors.forename: Matthias
authors.initials: M
authors.lastname: Egger
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Bern, Finkenhubelweg 11, 3012, Bern, Switzerland. ben.spycher@ispm.unibe.ch.
authors.forename: Ben D
authors.initials: BD
authors.lastname: Spycher
mesh_terms: D000293:Adolescent; D019352:Censuses; D002648:Child; D002675:Child, Preschool; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D011157:Population Dynamics; D011158:Population Growth; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000453:epidemiology* / Q000209:etiology*; D012959:Socioeconomic Factors; D013557:Switzerland / Q000453:epidemiology; D014505:Urban Population
keywords: Children; Cohort study; Leukaemia; Population mixing; Switzerland