The material covered in this Review is based on an extensive literature search and participation in expert meetings during the writing and updating of guidelines for the treatment of chronic obstructive pulmonary disease, along with many years of research in the area. We did a systematic Medline search for articles in English or with English abstracts with the keywords: “COPD” or “emphysema” or “chronic bronchitis” AND “prevalence” or “burden” or “risk factors” or “cost” or “morbidity” or
ReviewGlobal burden of COPD: risk factors, prevalence, and future trends
Section snippets
Definition
The working definition of COPD, as noted in the 2006 update of the Global Initiative for Obstructive Lung Disease (GOLD) guidelines, is that COPD is “a preventable and treatable disease with some significant extrapulmonary effects that may contribute to the severity in individual patients. Its pulmonary component is characterised by airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with an abnormal inflammatory response of the lungs to
Disease classification
COPD can be classified with respect to both phenotype and disease severity. It is a heterogeneous disease process that varies greatly from person to person with respect to lung pathology, natural history of disease, and comorbidity. A result of this heterogeneity is that different researchers have championed alternative hypotheses about COPD development over the past four decades: the British hypothesis stated that the presence of cough and sputum was the key factor in COPD,22 and the Dutch
Risk factors
Risk for COPD is related to an interaction between genetic factors and many different environmental exposures, which could also be affected by comorbid disease. Risk factors for the disease are described below.
Prevalence estimates
Two reviews have been published58, 59 in which the prevalence of COPD was noted to be highly variable, probably because of differences in methods for establishment of disease prevalence. Figure 4 shows the findings from the 12 sites of the BOLD study26 and the five sites in the Latin American Project for the Investigation of Obstructive Lung Disease (PLATINO) study.60 These estimates, even with identical methodologies, show a large amount of variability. For example, in the BOLD study,26 GOLD
Morbidity and mortality
Additional measures of the burden of COPD, such as morbidity, mortality, and costs, present challenges similar to those seen in attempting to measure disease prevalence. Table 3 shows WHO estimates of deaths and disability-adjusted life years attributable to COPD for the world's 25 most populous nations.1 This table highlights some of the difficulties with these other measures of COPD. For example, the estimated COPD death rate in Japan of 4·4/100 000 is nearly 30 times lower than that in China
Future trends
When Calverley and Walker reviewed COPD in 2003 they made some predictions about progress in disease.2 With respect to pathogenesis, they forecast that there would be greater phenotypic characterisation of COPD, identification of candidate susceptibility genes, clarification of the basis of steroid resistance, and enhanced animal models of the disease. With respect to clinical characteristics, they predicted that there would be better methods of detecting flow limitation and staging systems
Conclusion
Our knowledge of COPD has grown over the past few years. Additional questions are raised by this new knowledge, which are discussed here. One of the biggest advances in COPD is greater understanding of disease burden in different countries and cultures. Publication of data from the PLATINO60 and BOLD26 studies is vital to establish how important COPD is, particularly in view of the disease's consistent underdiagnosis at sites where it has been investigated.76, 77, 78 Other relevant components
Search strategy and selection criteria
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