Interpreting COPD prevalence estimates: What is the true burden of disease?

Study objectives: To summarize the available data on COPD prevalence and assess reasons for conflicting prevalence estimates in the published literature. Design: We reviewed published studies that (1) estimated COPD prevalence for a population, and (2) clearly described the methods used to obtain the estimates. Results: Thirty-two sources of COPD prevalence rates, representing 17 countries and eight World Health Organization-classified regions, were identified and reviewed. Prevalence estimates were based on spirometry (11 studies), respiratory symptoms (14 studies), patient-reported disease (10 studies), or expert opinion. Reported prevalence ranged from 0.23 to 18.3%. The lowest prevalence rates (0.2 to 2.5%) were based on expert opinion. Sixteen studies had measured rates that could reasonably be extrapolated to an entire region or country. All were for Europe or North America, and most fell between 4% and 10%. Conclusions: There is considerable variation in the reported prevalence of COPD. The overall prevalence in adults appears to lie between 4% and 10% in countries where it has been rigorously measured. Some of the variation attributed to differences in risk exposure or population characteristics may be influenced by the methods and definitions used to measure disease. Spirometry is least influenced by local diagnostic practice, but it is subject to variation based on the lung function parameters selected to define COPD.