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The effect of respiratory tract infections on reported asthma symptoms

Section of Epidemiology, Department of Population Health Sciences, National Institute of Public Health, Oslo, Norway, wenche.nystad{at}folkehelsa.no

Per Nafstad

Section of Epidemiology, Department of Population Health Sciences, National Institute of Public Health, Oslo, Norway

Jouni J. K. Jaakkola

Environmental Health Program, The Nordic School of Public Health, Göteborg, Sweden

Background: Wheezing and chest tightness is associated with respiratory tract infections. Thus the occurrence of respiratory tract infections may infl uence the prevalence of asthma. Aims: To assess the strength of relation between two main symptoms of asthma and the prevalence of respiratory tract infections in children with and without asthma. Methods: The study population was 3,796 children, four years of age, whose parents had answered a questionnaire on respiratory symptoms and asthma. The prevalence of wheezing and chest tightness in the last 12 months and four weeks was estimated according to the occurrence of respiratory tract infections during the corresponding time periods; 95% confi dence intervals of the prevalence and the statistical signifi cance of the differences in the prevalence by using chi-square test were calculated. Results: The prevalence of wheezing and chest tightness was higher in children who had experienced respiratory tract infections than in those who had not. The prevalence of wheezing was 17.5% among children who had experienced bronchitis and 3.0% among children whom had not ( p<0.001). The prevalence of chest tightness in the last 12 months was 3.7% (95% CI 3.1- 4.1) among children without asthma and 59.3% (95% CI 53.4- 65.2) among children with asthma (p<0.001). The prevalence of wheezing and chest tightness increased with increasing number of different types of respiratory tract infections among children without asthma (p<0.001) and tended to be so among children with asthma. Conclusions: These findings have implications for the interpretation of results from epidemiological studies using respiratory symptoms as a health-related outcome of asthma.

Key Words: asthma • epidemiology • infections • wheezing.

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