Incidence rate of adult-onset asthma in relation to age, sex, atopy and smoking: a Swedish population-based study of 15813 adults.
METHODS
Our knowledge about asthma incidence in an adult population is limited. The aim of the present investigation was to estimate the incidence rate of adult-onset asthma in relation to age, sex, atopy and smoking in a random population sample.


METHODS
A random sample of 20000 subjects 20 to 50 years of age was investigated using a short respiratory questionnaire. It was answered by 15813 persons. Adult-onset asthma was defined as a positive response to 'physician-diagnosed' asthma from 16 years of age. Subjects were also asked to report the year of asthma diagnosis, and also, when relevant, the year of smoke-start and smoke-stop. Incidence rates of adult-onset asthma and incidence rate ratios (IRR) were calculated.


RESULTS
The incidence rate of adult-onset asthma among females was 1.3 cases/1000 person-years compared with 1.0/1000 person-years for males (IRR 1.3, 95% confidence interval [CI] 1.0-1.6). The incidence rate was high (3.0/1000 person-years) among females aged 16-20 years. There was a strong association between the incidence rate of adult-onset asthma and hay fever, atopic dermatitis and family history of atopy. Compared with never-smokers, the IRR for female smokers was 1.6 (95% CI 1.1-2.2), while for male smokers it was unity. Both male and female ex-smokers had moderately increased rate ratios, of 1.5 and 1.1, respectively.


CONCLUSIONS
In this retrospective study, reported atopic symptoms and family history of atopy were strongly associated with incidence of adult-onset asthma. Tobacco smoking may be associated with an increased incidence rate of adult-onset asthma, especially among women.
Torén
K
K
Department of Respiratory Medicine and Allergology, Sahlgrenska University Hospital, Göteborg, Sweden. Kjell.Toren@medicine.gu.se
Hermansson
B A
BA
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D001249:Asthma / Q000453:epidemiology*; D005260:Female; D006801:Humans; D006967:Hypersensitivity; D015994:Incidence; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012307:Risk Factors; D012737:Sex Factors; D012907:Smoking; D013548:Sweden / Q000453:epidemiology