Can age and sex explain the variation in COPD rates across large urban cities? A population study in Canada

OBJECTIVE: To measure the prevalence of chronic obstructive pulmonary disease (COPD) and determine the effect of age and sex on the variation in prevalence across major cities within the same country and health care system. METHOD: We used the Burden of Obstructive Lung Disease (BOLD) methodology to estimate the prevalence of COPD in adults aged 40 years in different Canadian cities. The study used interviewer-administered questionnaires an respiratory, smoking and occupational history, medication use and comorbidities. Post-bronchodilator spirometry was used to classify subjects. We determined the prevalence and severity of COPD with and without adjustments for age and sex distribution across different cities. RESULTS: The study population was 3042. Overall, 16.7% (95%CI 14.8-18.7) of study subjects met the criteria for Global Initiative for Chronic Obstructive Lung Disease (GOLD) severity Stage 1 or higher. The prevalence according to the criteria for the lower limits of normal of the ratio forced expiratory volume in 1 second/forced vital capacity was 11.6% (95%CI 9.9-13.3). COPD prevalence varied by severity across site (P = 0.0025). After age-sex adjustment, the variation disappeared (P > 0.16). CONCLUSION: Age and sex differences account for most of the heterogeneity in COPD estimates across large cities within the same country. Adjustments for age and sex are essential in comparing COPD rates across the country.