An interview study to estimate prevalence of asthma and chronic bronchitis. The obstructive lung disease in northern Sweden study.

A questionnaire of respiratory symptoms and diseases completed by 6610 adults in 3 age cohorts (35-36 y; 50-51 y and 65-66 y) in northern Sweden was followed-up by interview and lung function testing of 1243 subjects with asthmatic or bronchitic symptoms and 263 subjects assessed from the postal questionnaire as being healthy. We report the results of this follow-up study. According to the criteria used, 292 subjects (5.1% of the original study sample) were diagnosed as having asthma. Out of the 1243 subjects 334 (5.9% of the original study population) were diagnosed as having chronic bronchitis. However, examination of the 263 subjects who were healthy according to the postal questionnaire showed that elderly smokers, in particular, under-reported bronchitic symptoms; taking this into account, the prevalence of chronic bronchitis is estimated to be of the order of 9%. Diagnostic difficulties were noted in 70 subjects (corresponding to 1.2% of the original study sample) in whom asthma or chronic bronchitis were strongly suspected. Further investigation of these subjects was considered necessary. In this cross-sectional study, FEV1 < 80% of predicted values was found in 36% of subjects diagnosed as having asthma and in 31% of those with chronic bronchitis. Among subjects with attacks of breathlessness and wheezing, diagnostic criteria often used for asthma in questionnaire studies, 70% were diagnosed as having asthma. Of those with chronic productive cough, 62% were diagnosed as having chronic bronchitis. We consider that trained nurses provide reliable data that may be used in epidemiological surveys of obstructive lung diseases.