Prevalence of respiratory symptoms in an unpolluted area of northern Italy.

Using a multistage stratified geographic cluster sample of households living in an unpolluted area of Northern Italy (near Venice), we enrolled 3289 inhabitants (aged 8-64 yr) for a longitudinal respiratory study. During the first cross-sectional survey, before the start of operation of a large oil-burning thermoelectric power plant, they completed a standardized administered questionnaire and performed several lung function tests. In the whole sample, dyspnoea grade 1 (11%), chronic cough and chronic phlegm (9%) were the most frequent respiratory symptoms; all the symptoms except dyspnoea were more prevalent in males than in females. Smokers (S) showed higher prevalence rates than ex-smokers (ES) and nonsmokers (NS), especially in males. In both sexes, the frequency of respiratory symptoms increased with increasing smoking as assessed by pack-years. An inverse relationship between prevalence of symptoms and socio-economic status was also observed. All tests of lung function were significantly impaired in S compared with NS in males; single-breath CO diffusing capacity and slope of alveolar plateau but not spirometric indices were significantly impaired in female S compared to female ES and NS. Finally, our prevalence rates were lower than in other epidemiological surveys: this result may be ascribed to the low levels of air pollution measured in the area.