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Disease in childhood and the impact of childcare

Mads Kamper-Jørgensen  


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Accepted by: Faculty of Health Sciences University of Copenhagen
Defended on: August 30, 2007
Official opponents: Freddy Karup Pedersen , Henrik Toft Sørensen , Per Magnus
Tutors: Jan Wohlfahrt , Christine Stabell Benn

Published in the PhD Database: September 4, 2007


English abstract
The present PhD thesis is based on five epidemiological studies of Danish register data regarding infection-related hospitalizations, childhood acute lymphoblastic leukemia (ALL) and attendance to childcare facilities in children aged 0-5 years in the period 1989-2004. The overall aim of the thesis was to study the impact of childcare attendance on disease in childhood on a short and a long-term basis, respectively. Short-term impact of childcare attendance was studied using hospitalizations for acute respiratory infections (ARI) as outcome, whereas ALL was studied to evaluate the long-term impact of childcare.
Initially, temporal trends in the incidence of hospitalizations for childhood infections in the period 1980-2001 in Denmark were characterized. We found an increase in the incidence of hospitalizations for infections, almost exclusively driven by short-term hospitalizations in 0-1-year-old children. Secondly, we described the creation of, the information available in, and the potential of the Childcare Database, containing more than 1 million children and created for the purpose of the present thesis. Thirdly, we assessed the short-term impact of childcare attendance on ARI. We found that childcare attendance was associated with an excess risk of ARI hospitalization, but only in 0-2-year-olds, during the first period of enrollment and in children not living with other children. Fourthly, we studied factors related to clustering of ARI in childcare facilities. We found that ARI hospitaliza-tions cluster among children in childcare facilities. Clusters involved 0-2-year-olds and boys as first hospitalized child relatively more often than other children. Finally, we studied whether attendance to childcare early in life was associated with childhood ALL. We found childcare attendance during the first two years of life to entail a reduced risk of childhood ALL and the studied child and family characteristics seemed to play a minor role in the as-sociation between childcare attendance and childhood ALL.

We have confirmed an increased infection hospitalization incidence over time, documented the establishment of the Childcare Database, and confirmed that childcare attendance is associated with an increased risk of ARI hospitalization and a decreased risk of childhood ALL. The thesis contributes with new knowledge by identifying subgroups of children involved in the increased infection hospitalization incidence over time, and by demonstrating that the association between childcare attendance and ARI hospitalization varies with characteristics of the child and the child¿s family, whereas these characteristics seem to play a minor role in the association between childcare attendance and childhood ALL.



Danish abstract
Nærværende ph.d.-afhandling er baseret på fem epidemiologiske studier af danske registerdata vedrørende infektionshospitaliseringer, akut lymfoblastisk børneleukæmi (ALL) og pasning af 0-5-årige børn i perioden 1989-2004. Det overordnede formål med afhandlingen var at studere betydningen af børnepasning for børnenes sygelighed på henholdsvis kort og lang sigt. Udfaldet i studierne af betydningen på kort sigt var hospitalisering for akut luftvejsinfektion (ARI), mens betydningen på lang sigt blev vurderet for ALL.
Indledningsvis karakteriserede vi udviklingen i infektionshospitaliseringer blandt børn i perioden 1980-2001 i Danmark. Vi fandt en stigning i incidensen af infektionshospitaliseringer, næsten udelukkende drevet af korttidsindlæggelser blandt 0-1-årige børn. Dernæst beskrev vi dannelsen af, og de tilgængelige informationer i ¿The Childcare Database¿, som omfatter mere end 1 million børn. Databasen blev dannet til brug i artiklerne i nærværende ph.d.-afhandling. Herefter vurderede vi korttidseffekten af børnepasning på risikoen for ARI-hospitalisering. Vi fandt at børnepasning medførte en øget risiko for ARI-hospitalisering, men kun blandt 0-2-årige børn, i løbet af de første seks måneder efter indmeldelse i en børnepasningsordning og blandt børn som ikke boede sammen med andre børn. Herefter studerede vi faktorer relateret til clustering af ARI-hospitaliseringer i børnepasningsordninger. Clusters involverede 0-2-årige og drenge som først hospitaliserede barn relativt oftere end andre børn. Endelig studerede vi, om børnepasning tidligt i livet var associeret med risiko for ALL. Vi fandt, at børnepasning i de første to leveår nedsatte risikoen for ALL. De studerede karakteristika ved barnet og barnets familie havde ikke betydelig indflydelse på associationen mellem børnepasning tidligt i livet og ALL.

Vi har bekræftet en stigende incidens af infektionshospitaliseringer over tid, beskrevet dannelsen af ¿The Childcare Database¿ samt bekræftet, at børnepasning er associeret med en øget risiko for ARI hospitalisering og en nedsat risiko for ALL. Afhandlingen bidrager med ny viden ved at identificere undergrupper af børn, som er involveret i den stigende inci-dens af infektionshospitaliseringer over tid, og ved at demonstrere, at associationen mellem børnepasning og ARI hospitalisering afhænger af karakteristika ved barnet og barnets familie, hvorimod disse karakteristika ikke synes at have betydelig indflydelse på associationen mellem børnepasning og ALL.