BackgroundThe prevalence of asthma has increased both among children and adults during the latter half of the 20th century. The prevalence among adults is affected by the incidence of asthma in childhood but also in adulthood. Time trends in asthma incidence are poorly studied.AimThe aim was to study the incidence of adult-onset asthma from 1996–2006 and 2006–2016, and compare the risk factor patterns.MethodsWithin the Obstructive Lung Disease in Northern Sweden (OLIN) studies, two randomly selected population-based samples in ages 20–69 years participated in postal questionnaire surveys about asthma in 1996 (n=7104, 85%) and 2006 (n=6165, 77%), respectively. A 10-year follow-up of the two cohorts with the same validated questionnaire was performed, and n=5709 and n=4552, respectively, responded. Different definitions of population at risk were used in the calculations of asthma incidence. The protocol followed a study performed 1986 to 1996 in the same area.ResultsThe crude incidence rate of physician-diagnosed asthma was 4.4/1000/year (men 3.8, women 5.5) from 1996–2006, and 4.8/1000/year (men 3.7, women 6.2) from 2006–2016. When correcting for possible under-diagnosis at study entry, the incidence rate was 2.4/1000/year from 1996–2006 and 2.6/1000/year from 2006–2016. The incidence rates were similar across age groups. Allergic rhino-conjunctivitis was the main risk factor for incident asthma in both observation periods (risk ratios 2.4–2.6).ConclusionsThe incidence of adult-onset asthma has been stable over the last two decades, and on similar level since the 1980s. The high incidence contributes to the increase in asthma prevalence.
Asthma, type-1 allergy and related conditions in 7- and 8-year-old children in Northern Sweden: prevalence rates and risk factor pattern
