The Prevalence of Chronic Obstructive Pulmonary Disease (COPD) and the Heterogeneity of Risk Factors in the Canadian Population: Results from the Canadian Obstructive Lung Disease (COLD) Study

PURPOSE: To determine the spirometric-based prevalence of COPD across different regions in Canada and to evaluate the site heterogeneity of risk factors. PATIENTS AND METHODS: In this cross-sectional, population-based study, random samples of non-institutionalized adults aged ≥40 years were generated by random digit dialling. Participants answered an interviewer-administered questionnaire and performed spirometry before and after bronchodilator administration. COPD was defined as post-bronchodilator FEV(1)/FVC <0.70 (fixed ratio, FR) and as FEV(1)/FVC <5th percentile (lower limits of normal, LLN). Separate logistic regression models were used to compute the risk (adjusted odds ratio, aOR) for COPD. I(2) and Tau(2) analyses were used to evaluate heterogeneity. RESULTS: Out of 5176 (95%) participants, 4893 (47% male with mean age 56.6 years (95% confidence interval, 56.0–57.2)) had spirometry that satisfied ATS criteria. The population prevalence of COPD was 16.2% (95% CI, 14.5–17.8) by FR and 11.2% (95% CI, 9.7–12.6) by LLN. Male predominance in prevalence was shown by FR but not by LLN criteria. Patient characteristics associated with an increased risk of COPD included: age (OR 1.56; 95% CI 1.33–1.84); history of physician-diagnosed asthma (OR 3.30; 95% CI 2.42–4.49); and childhood hospitalization for respiratory illness (OR 1.81; 95% CI 1.17–2.80). In terms of smoking-related risk factors, current smoking status had the highest odds ratio (OR 3.49; 95% CI 2.55–4.80). Variance in prevalence among sites was significantly reduced by adjusting for risk factors in Tau(2) analyses. Higher odds of exposure for each risk factor was found in more severe COPD, suggesting that a higher risk could be linked to the development of severe disease. CONCLUSION: This study reports the population prevalence of COPD in nine urban cities which collectively represent the majority of the Canadian population and demonstrates that heterogeneity in prevalence among sites is substantially explained by variation in associated risk factors for COPD.