Incidence and remission of asthma in schoolchildren: Report from the obstructive lung disease in northern Sweden studies

Objective. An increasing prevalence of asthma has been reported worldwide a s well as in Sweden. In 1996, the prevalence of asthma and type 1 allergy w as investigated in a cohort of 3525 children 7 and 8 years old in 3 areas o f northern Sweden. The aim of the present study was to estimate the inciden ce of asthma and to identify risk factors for incident cases over 1 year. Methods. The study started with a parental questionnaire, the International Study of Asthma and Allergies in Childhood questionnaire with additional q uestions, a skin prick test, and a validation study. The cohort was followe d up after 1 year with the same questions. The response rate to the questio nnaire was 97% in 1996, and 3339 children (97%) participated both in 1996 a nd 1997. Results. The incidence of physician-diagnosed asthma was 0.9/100/year; of w heezing, 3.8/100/year; and of new frequent or daily users of asthma medicin es, 1.1/100/year. There was no difference by sex. The risk factor pattern b ased on incident cases of asthma was different from that based on prevalent cases. Significant risk factors for incident asthma were a positive skin t est (odds ratio [OR]: 9.3; 95% confidence interval [CI]: 3.8-22.7); low bir th weight (OR: 7.4; 95% CI: 2.2-24.5); and family history of asthma (OR: 2. 6; 95% CI: 1.1-6.3). Having or having had pets at home was associated with a decreased risk for asthma and wheezing based on prevalent cases, although it was associated with an increased risk for incidence of wheezing (OR: 2. 9; 95% CI: 1.3-6.2). Remission of asthma, which was reported by 10% of the children with current asthma during 1 year, was associated with a negative skin test. Conclusion. The incidence of asthma at the age of 8 years was high, but rem ission was also common. Important risk factors for the development of asthm a at this age were type 1 allergy, low birth weight, and family history of asthma. Furthermore, the results suggest that in a region where sensitivity to domestic animals is a strong risk factor for asthma, the presence of pe ts in the home may have different effects in early childhood compared with later in childhood.