Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Epidemiology and Biostatistics

Supervisor

Karp, Igor

Abstract

Asthma causes substantial public health burden. An enhanced understanding of asthma burden, asthma course and identification of intervenable risk factor is warranted.

The objectives of this research were to: 1) examine the age, period and cohort effects on asthma prevalence among Canadian adults during 1994–2011 (manuscript one); 2) identify the trajectories of asthma exacerbation and their predictors in children with incident asthma (manuscript two); and 3) examine the effect of maternal gestational diabetes mellitus on the risk of asthma in offspring (manuscript three).

Longitudinal data from 13,616 individuals in the National Population Health Survey, household component were used to address objective one using generalized estimating equations. Data from 403 children with asthma in the National Longitudinal Survey of Children and Youth (NLSCY) were used to address objective two using latent class growth modeling and multinomial logistic regression. Pooled logistic regression was performed on data from 19,933 children in the NLSCY to address objective three.

By age, asthma prevalence was 12% in 20-year-olds, 6% in 50–60-year-olds, and 8% in 80-year-olds in Canadian adults. By period, asthma prevalence increased from 5% in 1994/1995 to 11% in 2010/2011. There was some evidence of cohort effect on asthma prevalence. Three distinct trajectories of asthma exacerbation were identified in children with incident asthma: low increasing (21.3% of children), medium decreasing (45.8% of children) and high decreasing (32.8% of children). Number of siblings at home and age at asthma diagnosis predicted trajectory group membership. The adjusted hazard ratio for the association between maternal gestational diabetes mellitus and incident asthma in the offspring was 1.25 (95% confidence interval [CI]: 1.03, 1.51).

Our findings suggest the presence of age, period and cohort effects on prevalence of asthma in Canadian adults. Children with incident asthma apparently follow three distinct trajectories of asthma exacerbations. Gestational diabetes mellitus appears to increase the risk of asthma in the offspring. The findings from this research provide further insights into trends in asthma burden in Canadian adults, asthma exacerbation trajectories in children that would aid physicians in prognosticating its course, and potential opportunity for prevention of asthma in children.

Summary for Lay Audience

Asthma causes a huge health burden. A better understanding of asthma course and its risk factors is needed. First, we studied the prevalence of asthma by age and time in adults. We then researched the patterns of an asthma attack and their associated factors in children with asthma. We looked if mothers' diabetes during pregnancy increased the risk of asthma in children. We used data from two Canadian national surveys. Our study began with 13,616 adults, 403 children with asthma and 19,933 children without asthma.

Asthma prevalence in adults was 12% at 20 years, 6% at 50–60 years and 8% at 80 years. Asthma prevalence increased from 5% in 1994/1995 to 11% in 2010/2011. Such pattern over time differed by age. Three different patterns of asthma attack course were found in children with asthma. The patterns were: a) low increasing (21.3%), b) medium decreasing (45.8%) and c) high decreasing (32.8%). Number of siblings at home and age at asthma diagnosis were associated with both medium decreasing and high increasing patterns. Diabetes during pregnancy increased the chance of asthma in children.

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