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Background: Although remission occur, childhood-onset asthma may persist until adulthood. Since few longitudinal population-based studies have followed a cohort from childhood until adulthood, the knowledge on predictors of persistence of asthma is sparse. Aim: To estimate persistence of asthma from 8 to 28 years and its associated factors. Methods: Within the OLIN (Obstructive Lung Disease in Northern Sweden) studies, a cohort was recruited in 1996 (age 8y, n = 3430) and followed annually with questionnaires about asthma and risk factors until 19y. Clinical examinations included skin prick tests (at 8, 12 and 19y) and lung function tests (17 and 19y) whereof a subsample performed bronchial hyperreactivity test. We identified n = 248 with asthma at 8y whereof 170 (69%) participated in a follow-up at 28y (73% of possible to invite). Results: Of the 170 participants at 28y, 105 (61.8%) had persistent asthma (women: 49/76, 64.5%; men: 56/94, 59.6%, p = 0.513). Factors collected at recruitment: allergic sensitization (OR7.8, 95%CI 3.0–20.2), severe respiratory infection (OR2.6, 95%CI 1.1–6.3) and higher asthma severity score (OR1.6, 95%CI 1.1–2.4) were associated with asthma at 28y after adjustment for sex, family history of asthma, breastfeeding <3 months and eczema. Replacing allergic sensitization with rhinoconjunctivitis in the model yielded OR3.4 (95%CI 1.5–8.0). Bronchial hyperreactivity at age 17y associated with asthma at 28y (OR9.0, 95%CI 1.7–47.0). Conclusions: Among children with asthma onset by 8y, 62% still had asthma at age 28 years. Persistent asthma was associated with allergic sensitization, rhinoconjunctivitis, severe respiratory infection, a more severe asthma and bronchial hyperreactivity.

Aim: to update the knowledge on the epidemiology of asthma with onset in childhood and adulthood as well as examine the importance of risk factors in early childhood and clinical characteristics on the incidence and prognosis of asthma. Methods: The thesis is based on the epidemiological research program Obstructive Lung Disease in Northern Sweden (OLIN) studies. Pediatric cohort: recruited in 1996 (age 8y, n=3430, 97% of invited) and followed annually by questionnaire about asthma, allergy and risk factors until 19y and a postal questionnaire at 28y. Clinical examinations included skin prick tests (SPT at 8, 12 and 19y) and spirometry (19y). Adult cohort: 309 adults (age 20–60y) with asthma onset in the last 12 months were recruited 1995-99 and re-examined in 2012-14 (n=205). Structured interviews, spirometry and SPT were performed at recruitment and follow-up and bronchial hyperreactivity (BHR) at recruitment. Results: The asthma incidence rate was 10-13/1000/year in childhood and adolescence and 6/1000/year in young adulthood. Several risk factors in early life were associated with asthma onset in childhood, adolescence and young adulthood, e.g. family history of asthma, <3 months breastfeeding, rhinoconjunctivitis and positive SPT at 8y, while low birthweight, maternal smoking during pregnancy, severe respiratory infections and eczema were associated with onset in childhood and adolescence. Among those with asthma at 8y, 62% still had asthma at 28y and this was associated with positive SPT, rhinoconjunctivitis, severe respiratory infection in childhood, and bronchial hyperreactivity (BHR) in adolescence. Coexistence of asthma, rhinitis and eczema increased by age, especially among those with a positive SPT. However, having all three conditions was uncommon. In the 15y follow-up adult onset asthma, 89% had persistent asthma. Better lung function at recruitment and less severe BHR was associated with remission. Remission rate of adult onset asthma was <1% pe