Diverging trends of chronic bronchitis and smoking habits between 1998 and 2010
STUDY OBJECTIVES To determine the 10-year cumulative incidence of COPD in a cohort of subjects with respiratory symptoms (Global Initiative for Chronic Obstructive Lung Disease [GOLD] stage 0) using the British Thoracic Society (BTS) and GOLD spirometric criteria. Furthermore, we sought to evaluate risk and gender factors for incident COPD. DESIGN AND SETTING A postal questionnaire was administered in 1986 to all 6,610 subjects in eight areas of northern Sweden who had been born in 1919 to 1920 (group 1), 1934 to 1935 (group 2), and 1949 to 1950 (group 3). The response rate was 86%. All of the subjects reporting respiratory symptoms were invited to participate in a structured interview and pulmonary function test (PFT), and 1,506 (91%) participated. In 1996, 90% could be traced for follow-up, of whom 1,165 (86%) of the invited subjects participated and 1,109 subjects (534 women) were able to perform technically adequate PFTs in both 1986 and 1996. RESULTS The 10-year cumulative incidence of COPD was estimated at 8.2% (using BTS criteria) and 13.5% (using GOLD criteria). Significant risk factors for incident COPD (using BTS and GOLD criteria) in a multivariate analysis were higher age (group 1 odds ratio [OR]: BTS criteria, 3.49; GOLD criteria, 3.37; group 2 OR: BTS criteria, 4.50; GOLD criteria, 5.70) and smoking (OR: BTS criteria, 5.37; GOLD criteria, 4.56), but not gender or heredity. Respiratory symptoms were significantly associated with incident COPD when added to the same model. In analogous analyses that were conducted separately for men and women, smoking yielded an OR of 8.52 among women (95% confidence interval [CI], 3.43 to 21.2) compared with 3.14 among men (95% CI, 1.26 to 7.84). The symptoms cough, sputum production, and chronic productive cough reached statistical significance in women, while dyspnea and wheeze did so in men. CONCLUSION In this cohort, the 10-year cumulative incidence of COPD was 8.2% (using BTS criteria) and 13.5% (using GOLD criteria). Increasing age, smoking, and bronchitic symptoms, but not gender, were risk factors for incident COPD. GOLD stage 0 therefore appears to identify subjects who are at risk of COPD, but men and women presented different risk profiles.