CHANGING PREVALENCE OF ASTHMA IN SCHOOL-CHILDREN - EVIDENCE FOR DIAGNOSTIC CHANGES IN ASTHMA IN 2 SURVEYS 13 YRS APART

It is still unclear whether the reported increase in the prevalence of asthma is real or due to changes in diagnostic criteria. The objectiv es of this study were to compare the prevalence of diagnosed asthma wi th the prevalence of respiratory symptoms, and to compare the associat ion between asthma and other atopic diseases in 1981 and 1994. The stu dy populations comprised randomly selected school classes in Oslo in 1 981 (n=1,772) and 1993 (n=2,577). The main outcomes in these comparabl e cross-sectional studies of children, 6-16 yrs of age, were parent-re ported prevalence of diagnosed asthma, respiratory symptoms, eczema an d hay fever. The questionnaire was identical in 1981 and 1994. The res ponse rates were 94% (1,674 out of 1,772) in 1981 and 85% (2,188 out o f 2,577) in 1994. The lifetime prevalence of asthma increased from 3.4 % in 1981 to 9.3% in 1994; odds ratio (OR) 2.9 (95% confidence interva l (95% CI) 2.1-4.0) comparing 1994 to 1981. The prevalence of occasion al wheezing increased from 9.0 to 10.8%; OR 1.2 (95% CI 1.0-1.5), and attacks of wheezing from 3.7 to 6.8%; OR 1.8 (95% CI 13-2.5). Survival analyses for 3 year birth cohorts showed that asthma was more readily diagnosed in the latest birth cohort (1985-1988). The association bet ween asthma and other atopic diseases decreased during the period unde r study. The increase in diagnosed asthma and respiratory symptoms sup ports a true increase in asthma. However, the larger increase in diagn osed asthma than wheezing and a reduced association between asthma and other atopic diseases suggest that the increase in asthma may be expl ained, in part, by changes in diagnostic criteria.