ArticlesInternational variation in the prevalence of COPD (The BOLD Study): a population-based prevalence study
Introduction
Chronic obstructive pulmonary disease (COPD) is an important and growing cause of morbidity and mortality worldwide.1, 2, 3 The WHO Global Burden of Disease Project1, 2 estimated that COPD was the fifth leading cause of death worldwide in 2001 and will be the third leading cause by 2020. The growing burden of COPD is partly due to the ageing of the world's population and partly to the continued use of tobacco, which is the most important risk factor for this disease.2, 3
WHO estimates of the burden of COPD are based on the little data available for both COPD and present patterns of cigarette smoking. Available information about COPD has not been obtained by consistent methods, and evidence suggests that rates of disease are generally underestimated.4, 5 Accurate estimates of the prevalence of COPD and its risk factors would help guide future projections of the worldwide burden of this disease and assist public-health officials in planning to meet the growing demand for services that rising COPD rates will create.
The Burden Of Obstructive Lung Disease (BOLD) Initiative6 developed standardised methods for estimating COPD prevalence and for obtaining information about risk factors. These methods can be used in countries at all levels of development and were developed in conjunction with The Latin American Project for the Investigation of Obstructive Lung Disease (PLATINO),7 which was undertaken in five Latin American countries.
Our aim was to measure the worldwide prevalence of COPD and its risk factors in adults aged 40 years and older and to investigate variation in prevalence across countries by age, sex, and smoking status.
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Study design and participants
A description of the design and rationale for the BOLD initiative has been published elsewhere.6 Participants were recruited with use of population-based sampling plans. Questionnaires were used to obtain information about respiratory symptoms, health status, exposure to risk factors, and economic data for the burden of COPD. Prebronchodilator and postbronchodilator spirometry testing was also done for all participants. Data were entered into a secure web platform maintained by the BOLD
Results
At the 12 study sites, 9425 study participants completed core questionnaires and postbronchodilator spirometry (table 1). Cooperation rates were slightly higher than were response rates, which ranged from 14% to 87%. The lowest response and cooperation rates were in the random-digit-dialling sites (Vancouver and Kentucky; table 1), which reflect the large number of phone numbers for which either no contact was made or the respondent hung up before eligibility was confirmed.
Usable spirometry
Discussion
Our study has shown heterogeneity in the prevalence and staging of COPD both across sites and between men and women within sites. These differences can be at least partly explained by site and sex differences in the prevalence of cigarette smoking and other risk factors. The prevalences of COPD reported in this study tended to be greater than those typically reported in previous studies,4, 5 but are generally similar to those reported in the PLATINO Study.7 PLATINO, which used similar methods
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