Prevalence of respiratory symptoms: marked differences within a small geographical area

BACKGROUND: Geographical differences in prevalence of respiratory symptoms have been reported between countries in the EC Respiratory Health Survey (ECRHS). The differences between two neighbouring centres in the Antwerp area were surprising. We therefore extended the screening phase of this study to four other areas with different features in this region. METHODS: Methods and questionnaires of the first phase of the ECRHS were used to estimate prevalence rates of respiratory symptoms in all areas. Information on some major personal and environmental risk factors was also obtained. RESULTS: Higher prevalence rates of both respiratory symptoms and personal risk factors were recorded in Urban Antwerp, Berendrecht-Zandvliet (harbour area) and Zwijndrecht (industrial area) than in Suburban Antwerp, Essen and Kasterlee (both rural). Neither personal nor environmental risk factors could provide satisfactory explanations for the area differences in symptoms. CONCLUSIONS: These large differences between groups of subjects living within a small geographical area prove that estimations of prevalence rates of a whole country based on measurements of prevalence in one specific area should be interpreted very cautiously. Epidemiological research within small geographical areas may thus still prove as informative as comparisons between countries for elucidating causes for different asthma prevalence.