Between 1994 and 2001, 70,000 children under 11 years have been added to the growing cases of asthma, said the survey. "If you look at a class of 30 kids (there are) five or six kids with asthma in the class..." explains Dr. Sheldon Spier of the Alberta Children's Hospital.

But as the rates increase, recent numbers show that among children with asthma, less attacks occurred in the past year.

The probability of asthma attacks depends on the severity of the disease, said the survey that analysed data from the National Longitudinal Survey of Children and Youth. However, the proportion of children with high-severity symptoms has decreased from 41% in 1994-95 to 36% in 2000-01.

The study also reveals that boys, children in the Maritimes and kids living in a smoking environment were more likely to develop the disease.According to the American Centre for Disease Control and Prevention (CDC), asthma is a disease that affects the lungs, causing wheezing, breathlessness, chest tightness, and coughing.