Low prevalence of asthma in westernizing countries-myth or reality? Prevalence of asthma in Estonia--a report from the "FinEsS" study

The aim of this study was to examine the prevalence of asthma among adults in Estonia by using different diagnostic methods and criteria for the disease. In 1995-1996, a postal questionnaire was randomly distributed in three areas of Estonia to a representative sample of 22,579 subjects aged 15-64 years. The participation rate was 78%. A clinical follow-up study including structured interview, skin prick test, lung function, and methacholine test, was performed from 1997 to 2000 among randomly selected responders to the postal questionnaire. Of 2676 subjects, 53% participated. The prevalence of physician-diagnosed asthma for the postal questionnaire (PQ) was 2.7%, and in the same subjects for the structured interview (SI) 3.8%. Respiratory symptoms, except recurrent wheeze, were more common in the SI than PQ. Combinations of symptoms, except wheezing with breathlessness apart from cold, were more prevalent in the PQ responders. The prevalence of asthma defined by different symptom combinations varied from 5.4% to 8.2%. Among responders, 71-87% demonstrated bronchial hyperreactivity defined as methacholine reactivity=8 mg/mL. The symptom combinations used as surrogate variables for asthma were strongly associated with a positive skin test. The low prevalence of physician-diagnosed asthma probably reflects a considerable underdiagnosis of asthma in Estonia. Disease criteria for asthma based on symptom combinations together with hyperreactivity yielded a prevalence of 5%-8%, which is similar to the prevalence of asthma among adults in neighboring Western countries.