Changes in chronic respiratory symptoms in two populations of adults studied longitudinally over 13 years

Data from two longitudinal studies conducted in Cracow, Poland, and Tucson, Arizona, USA, were used to evaluate the differences in period prevalence, incidence and remission rates of respiratory symptoms between two populations, as well as to assess the between-cities similarities in the relationships of the symptoms to age and smoking habit. The analysis was based on data from 3,082 adult Cracow residents, interviewed twice 13 yrs apart, and from 1,452 Tucson adults, with mean period between initial and final survey of 12.2 yrs. Log-linear models were used to consider possible interactions of the symptoms, age, smoking, gender and city. The relationship of the symptoms to smoking was similar in both cities, after adjustment for age and gender, with at least doubled incidence rates of most symptoms in continuous smokers compared to lifetime nonsmokers. The between-population differences in the symptoms were related to age, indicating onset of bronchitic symptoms occurring earlier in life in Cracow, and of asthmatic symptoms in Tucson. These differences were due to factors other than tobacco smoking e.g. various types of ambient air pollution.