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Tuesday, June 4, 2013

Early Environmental Determinants of Asthma Risk in a High-risk Birth Cohort

Asthma is a complex disease resulting from both genetic and environmental influences. Some studies have shown that exposure to certain indoor particles (eg from tobacco smoke, dust mites, viruses, pets, etc) early in life seems to increase the chance of developing asthma. Others have found these same environmental exposures have no effect. The CAPPS (The Canadian Childhood Asthma Primary
Prevention Study) researchers wanted to look at environmental factors that influence the development of asthma in children who are genetically at higher risk of developing asthma.  

Children are genetically at higher risk of developing asthma if at least one parent or a sibling has asthma or, at least two of parents or siblings have allergies or eczema. 

Research question:
What factors increase the chances of high risk children developing asthma by 7 years of age?

Can certain changes in the environment protect these children from developing asthma?

What was done:
Researchers followed 380 mothers of high risk children from the third trimester of pregnancy till the child was 7 years old.

The families were randomly assigned to the intervention group or the control group.

Families were from Winnipeg and Vancouver

The intervention group: Researchers helped theses families reduce exposure to house dust mite, tobacco smoke, and pets in the home.  Breast feeding was encouraged and solids were delayed until the child was 6 months old.

The control Group: The control group followed the usual care with advice from their doctors and no input from researchers. 

Both groups' indoor environment was assessed during home visits before the birth of the child, and at 2, 4, 8, 12, 18, 24 months, and at 7 years after the birth. The prevalence of a specific respiratory virus (RSV) was also assessed over the first 2 years of life. At the age of 7 years all of the children were seen by a pediatric allergist for assessment.  Allergy skin tests were done.

18.7% of children were diagnosed with asthma by 7 years of age.

The following factors increased the chances of a child developing asthma:
  • The development of allergies (eczema, food or environmental allergies) in the first few years of life. 
  • Having a mother or older siblings with asthma. 
  • Being male. More boys than girls developed asthma. 
  • Living in Winnipeg. More children in Winnipeg developed asthma than in Vancouver, perhaps because children in Winnipeg had higher rates of allergies (51.1% vs 39.5%).  This may be related to climate differences and the indoor environment. 
  • The child having Respiratory Syncytial virus (RSV) infection in the first year of life.
  • Owning a dog in the first year of life.
  • What happens in the first year of life seems most important.
  • Children in the intervention group, where intervention measures were applied prior to birth and for the first year of life, had a significantly lower risk (14.9%) for developing asthma by the age of 7 years than the control group (23%).
  • Having a dog in the home and the child having an RSV infection both in the first year of life are more important than the same exposure in later years
  • It is not clear which intervention specifically made a difference.  The first year of life may be a “window of opportunity” for intervention measures to help prevent asthma in high risk children. 
  • Inherited risk factors ie: the presence of asthma in the mother, or older siblings, was the strongest predictor that the child would also develop asthma. 
  • The intervention measures undertaken (decreasing exposure to house dust mite, tobacco smoke, and pets in the home, increasing breast feeding delaying solids until the child was 6 months old) did not significantly change the effects of inherited risk factors or family history in the development of asthma. 

Pediatr Allergy Immunol 2008: 19: 482–489. Early environmental determinants of asthma risk in a high-risk birth cohort. Chan-Yeung M, Hegele RG, Dimich-Ward H, Ferguson A, SchulzerM, Chan H, Watson W, Becker A. 

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