A Health Surveillance Update on Canadian Children and Youth

Asthma Prevalence

Asthma is a chronic inflammatory disorder of the airways and one of the most prevalent chronic conditions in Canada.

Asthma is a chronic inflammatory disorder of the airways and one of the most prevalent chronic conditions in Canada.^(1,2) In 1993 alone, over $12 billion was spent on asthma in Canada.⁽³⁾ The prevalence of asthma is the total number of existing asthma cases in a population in a given time period. One method of estimating the prevalence of asthma among Canadian children and youth is through a self-reported or parent-reported diagnosis of asthma in population surveys. Since 1978, Statistics Canada has conducted several population surveys that have included questions related to asthma.

In the 1996-1997 National Population Health Survey, asthma was reported in 12.2% of children and youth less than 20 years of age in Canada.^(4,5) The prevalence was highest among 15-19 years olds (14%) and lowest among children less than 4 years of age (8.2%). However, there was high sampling variability in the under-4 year age category. In the 0-14 year age group, asthma was reported in 13.3% of boys compared with 9.5% of girls. In contrast, among 15-19 year olds, the prevalence was higher among girls than boys (14.9% vs. 13.2%).

As depicted in Figure 1, the prevalence of reported asthma has been increasing over time.^(4-7) It is unclear whether this trend reflects a true increase or is an artifact resulting from (a) changes in the likelihood of diagnosing asthma (a shift toward diagnosing asthma instead of other respiratory disorders, such as bronchitis) and/or (b) an increased awareness of asthma among the public and health professionals. As well, changes in the wording of the asthma questions in periodic surveys may affect the prevalence estimates obtained. Surveys conducted in 1978 and 1984 asked Do you have asthma?, ⁽⁶⁾ whereas the most recent population surveys specified as diagnosed by a health professional? ⁽⁵⁾ However, despite this more specific wording, the reported prevalence has increased.

* 1984 survey includes 0-14 years of age only
Source: Bureau of Cardio-Respiratory Diseases and Diabetes, LCDC⁽⁴⁾

Many acute attacks in asthmatic children are preventable. One household survey found that 47% of asthmatic school-aged children reported that household pets triggered or worsened their disease; 41% had a dog and 36% had a cat inside their home. Similarly, 54% of asthmatic children were exposed to second hand smoke, yet smoke was identified as worsening their asthma.⁽⁸⁾

Internationally, an increasing prevalence of asthma over time has also been noted.⁽⁹⁾ As depicted in Figure 2, the prevalence of asthma in the United States has nearly doubled from 1980 to 1993 among children 0-14 years old.⁽¹⁰⁾ Despite this increasing trend, the prevalence in the United States remains lower than the most recent prevalence estimates obtained from Canadian children and youth.

Source: Centers for Disease Control and Prevention, United States⁽¹⁰⁾

Data limitations
The prevalence estimates provided are limited by the self-reported nature of the data. Furthermore, various population surveys have used different questions and focused on different age groups, which limits the interpretation of the trend over time. In addition to these limitations, international comparisons may be affected by variations in clinical practice and diagnostic criteria in different countries.

Summary
Despite the limitations of the available data, the surveys suggest that asthma is a very prevalent condition among Canadian children and youth. Further prevention efforts to protect asthmatic children from environmental triggers may improve their health. Estimates of asthma prevalence obtained by future iterations of the National Population Health Survey, based on consistent questions and age categories, will provide valuable information on the nature and trend of asthma in Canada.

Unless referenced otherwise, asthma prevalence statistics are the product of the Bureau of Cardio-Respiratory Diseases and Diabetes, LCDC⁽⁴⁾

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