Remission of respiratory symptoms by smoking and occupational exposure in a cohort study.

Few studies have estimated the remission rates of respiratory symptoms in general populations. No community cohort studies have examined the impact of smoking cessation and previous dust or fumes exposure on the remission of respiratory symptoms. In the Hordaland County Study, an 11-yr community cohort (1985-1996/1997) from Western Norway, data from 2,819 subjects were used to examine the remission of six respiratory symptoms. The measured cumulative remission varied from 42.3% for morning cough to 58.4% for chronic cough. Smoking cessation was a significant predictor of remission of the cough symptoms and wheezing, with odds ratios (OR) (95% confidence intervals (CI)) varying from 2.2 (1.3-3.7) for wheezing to 6.2 (3.5-11.2) for morning cough, after adjustment for sex, age, pack-years smoked, previous dust or fumes exposure, and educational level. In those not previously exposed to dust or fumes, the adjusted OR (95% CI) for the remission of morning cough, phlegm cough, dyspnoea grade 2, attacks of dyspnoea and wheezing varied from 1.5 (0.9-2.5) for attacks of dyspnoea to 2.1 (1.1-3.9) for dyspnoea grade 2, as compared to those previously exposed to dust or fumes. This study suggests a beneficial effect of smoking cessation and an adverse effect of occupational exposure on the remission of respiratory symptoms.