Childhood asthma. Epidemiology, prevalence and risk factors

Abstract

Background and aim: Asthma is one of the most common chronic diseases among children often resulting in medical treatment, morbidity and reduced quality of life. It is therefore important to study factors associated with asthma development. Long-term follow-up studies within this research field are scarce. One aim of this thesis was to examine the prevalence of asthma and uncontrolled asthma in a long-term follow-up (12-year-olds). Furthermore, we wanted to study the risk factors for asthma development as well as the risk factors for having an uncontrolled asthma. We also aimed to investigate whether people’s behaviour regarding known factors associated with the risk of asthma changed over time. Finally, we aimed to assess the agreement between our questionnaire-based data compared with Swedish national registers. Methods: Data for the first three, and partly four, papers in this thesis were obtained from a prospective, longitudinal cohort study of children born in 2003 in the region of western Sweden. The parents answered questionnaires at six months and one, four, eight and 12 years of age. The response rate was 68.9% (4,987/7,241) at one year and 76.1% (3,637/4,777) at 12 years. Personal identity numbers (PIN) linked 3,634 children to the Swedish Prescribed Drug Register (SPDR) and the National Patient Register (NPR). Data for the fourth paper in this thesis were obtained from a prospective, longitudinal cohort study of children born in 2018 in the region of western Sweden. The parents answered questionnaires at six months and one year of age. The response rate was 41.5% (3,936/9,475) at one year of age. The questionnaires for both cohorts (2003 and 2018) were based on well-established validated questionnaires. Results: At 12 years of age, 6.4% reported current asthma and 15% of the asthmatic children were labelled as having uncontrolled asthma. Antibiotic treatment early in life was a risk factor for atopic asthma (OR 2.2, 95% CI 1.2-4.2) while a higher parental educational level was associated with better asthma control (OR 0.3; 95% CI 0.1–0.8) among the children at 12 years of age. The introduction of complementary feeding to infants of eggs, fish and gluten was made significantly earlier in the 2018 cohort compared with the 2003 cohort (p <0.01). We found good agreement between questionnaire-based data and SPDR data regarding asthma medication. Conclusion: The association between antibiotic treatment and an increased risk of atopic asthma suggests an immune mediated effect. A lower parental educational level was a risk factor for uncontrolled asthma and some families might need greater educational effort in order to achieve equivalent health for asthmatic children. The earlier introduction of complementary feeding in children born in 2018 compared with 2003 might possibly reduce the risk of asthma development. Finally, we conclude that parental questionnaires, if well-constructed, can provide reliable data on childhood asthma.