Intergenerational 20 year trends in the prevalence of asthma and hay feverin adults: the Midspan family study surveys of parents and offspring

Objective To estimate trends between 1972-6 and 1996 in the prevalences of asthma and hay fever in adults. Design Two epidemiological surveys 20 years apart. Identical questions were asked about asthma, hay fever, and respiratory symptoms at each survey. Setting Renfrew and Paisley, two towns in the west of Scotland. Subjects 1477 married couples aged 45-64 participated in a general populati on survey in 1972-6; and 2338 offspring aged 30-59 participated in a 1996 s urvey. Prevalences were compared in 1708 parents and 1124 offspring aged 45 -54. Main outcome measures Prevalences of asthma, hay fever, and respiratory sym ptoms. Results In never smokers, age and sex standardised prevalences of asthma an d hay fever were 3.0% and 5.8% respectively in 1972-6, and 8.2% and 19.9% i n 1996. In ever smokers, the corresponding values were 1.6% and 5.4% in 197 2-6 and 5.3% and 15.5% in 1996. In both generations, the prevalence of asth ma was higher in those who reported hay fever (atopic asthma). In never smo kers, reports of wheeze not labelled as asthma were about 10 times more com mon in 1972-6 than in 1996. with a broader definition of asthma (asthma and /or wheeze), to minimise diagnostic bias, the overall prevalence of asthma changed little. However, diagnostic bias mainly affected not-atopic asthma. Atopic asthma increased more than two-fold (prevalence ratio 2.52 (95% con fidence interval 1.01 to 6.28)) whereas the prevalence of non-atopic asthma did not change (1.00 (0.53 to 1.90)). Conclusion The prevalence of asthma in adults has increased more than twofo ld in 20 years, largely in association with trends in atopy, as measured in directly by the prevalence of hay fever. No evidence was found for an incre ase in diagnostic awareness being responsible for the trend in atopic asthm a, but increased awareness may account for trends in non-atopic asthma.