Asthma in school age:: prevalence and risk factors by time and by age

Background: Childhood is the most important age for asthma development. Recent reports indicate that the prevalence of asthma. in children has plateaued after having increased for decades. Aims: To study prevalence and risk factor patterns of asthma by age and by time. Methods: In 1996, all children in grade 1-2 (age 7-8) in three cities ill Northern Sweden were invited to an expanded International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. A total of 3430 children (97%) participated yearly until 2000 (age 11-12). A subset (n = 2454) was invited to skill-prick testing in 1996 and 2000 with 88% and 90% participation. In 2006, another cohort (n = 2704) was identified and studied by identical methods with 96% participation. A total of 1700 children (90% of invited) were skin-prick tested. Results and comments: From age 7-8 to 11-12, the prevalence of physician-diagnosed asthma increased, 5.7%-7.7% (P<0.01) while current wheeze decreased, 11.7%-9.4% (P < 0.01), indicating a less diverse spectrum of symptoms with age. The yearly remission from asthma was 10% (lasting remission 5%), largely determined by allergic sensitisation. Allergic sensitisation (OR 5) and a family history of asthma (OR 3) were important risk factors for asthma at age 7-8 and 11-12. However, several other significant risk factors at age 7-8 (low birth weight, respiratory infections and house dampness) lost importance until age 11-12. Maternal and paternal asthma were equally important risk factors (OR 3-4) at age 7-8. Sibling asthma was only a marker of parental disease. Future perspectives: Through comparison with the 2006 cohort, trends in prevalence and in risk factors from 1996 to 2006 will be studied.