Allergy t997:52: IO7l-IO7fi Primed in UK - «// rigtils reserved Copvrighl © Munksgaard 1997 ALLERGY ISSN 0I05-453S Incidence of asthma in adults - report from the Obstructive Lung Disease in Northern Sweden Study Ronmark E, Lundback B, Jonsson E, Jonsson A-C, Lindstrom M, Sandstrom T. Incidence of asthtna in adults - report frotn the Obstructive Lung Disease in Northern Sweden Study. Allergy 1997: 52: 1071-1078. © Munksgaard 1997. Incidetice studies offer a better opportunity to study risk factors for asthtna than do prevalence studies. However, tegular prospective follow-ups of large cohorts are difficult to perfonn, and that is why direct measurctnent ol' the iticidcnce rate of asthtna is almost itnpossible. Thus, cross-sectional follow- up studies of defined cohorts can be used to provide data on incidence. In 1986, a postal questionnaire survey on respiratory symptoms and diseases was performed in the northernmost provitice ot Sweden. Tlie population satnple cotiiprised all subjects born in 1919-20, 1934-5, and 1949-50 in eight representative areas of the province, which cotnpriscs 25% of the total area of Sweden. Completed atiswers were given by 5698 subjects (86%) of the 6610 subjects invited to the study. In 1992, the cohort was invited to a follow-up survey during the satne season as in 1986, and 6215 subjects were traced. Of the 5393 subjects who answered the questionnaire, 4932 had participated in the 1986 survey, or 87% of those who participated in 1986. For the period 1986-92, the cumulative incidences of asthtna were 4.9 and 5.0%, respectively, as assessed by the questions, "Have you ever had asthma?" and "Have you been diagnosed as having asthtna by a physician?" Thus, the results indicate a mean annual cumulative incidence of asthma of 0.8%. After correction of the results for subjects who were diagnosed as having asthma in the clinical part later in the 1986 study, the mean annual cumulative incidence of asthtna was found to be 0.5%. Risk factors were family history of asthma (OR 3.46) and current and fortner smoking, while female sex was a strong trend. E, Ronmark^"^ B, Lundback^ I E, Jonsson\ A,-C. Jonsson^ M. Lindstrom^ ^ T, Sandstrom^ " 'National Institute for Wori<ing Life, Department of Occupational Health, Respiratory Epidemiology Unit, Umea; ^OLIN Study Group, Central Hospital of Morrbotten, Boden; \ulea Health Care Center, Lulea; 'Department of Pulmonary Medicine and Allergy, University Hospital of Northern Sweden, Umea, Sweden Key words: asthma; epidemiology; incidence; adults. Bo Lundback National Institute for Working Life Department of Occupational Health Respiratory Epidemiology Unit S-907 13 Umea Sweden Accepted for publication 26 May 1997 Many cross-sectiotial prevalence studies on asthma have been reported in recent years. Most of these studies give a uniform picture of the increasing prevalence of asthma (1-3). However, cross-sectional studies are of limited interest when studying risk factors for asthma. Tliey express relationships or associations of uncertain value in the causality of asthma. Furthennore, cross-sectional studies give no or poor infortiiation of incidence, remission, and prognosis. Studies of incidence not only contribute to the descriptive epidemiology of asthtna but also offer a better opportunity than do prevaletice studies to assess risk factors for the disease. To measure an exact incidence rate in a general population is difficult and requires follow-ups of large represent- ative cohorts of the population under study over several years. Only a few prospective studies of asthma incidence have been reported in the literature, tnost of them on children and teenagers. Most published studies on adults are from the USA and include large register studies (4, 5) and conven- tional population-based studies (6-8), indicating annual incidetice rates of 1-4/fOOO person years. Tlie Tecumseh, Michigan study, which included physiciatis' examinations, gave a 4-year cumulative incidence of asthtna of 1% in the early 1960s (7). Tlie Tucson, Arizona studies reported an annual incidence of 0.4/100 person years from birth to old age with the lowest incidence in adolescents (8). The low incidence in adolescents and young adults 1071