Chronic Obstructive Pulmonary Disease: Epidemiology, Clinical Presentation, and Evaluation

Morbidity and Mortality

COPD is a leading cause of disease morbidity and mortality in the United States. The National Center for Health Statistics (NCHS) conducts ongoing surveillance of several health indicators nationally. The NCHS collects physician office visit data using the National Ambulatory Medical Care Survey [23], emergency department visit data and hospital outpatient data using the National Hospital Ambulatory Medical Care Survey [24], hospitalization data using the National Hospital Discharge Survey [25], and death data using the mortality component of the National Vital Statistics System [26]. The following data include the number and rate of COPD events in adults in the United States (using International Classification of Diseases, 9th Revision, Clinical Modification [ICD-9-CM], codes 490, 491, 492 and 496) in these data sets for the most recent years available.

In 2010, COPD was responsible for an estimated 10.3 million physician office visits, with a resulting age-adjusted rate of 494.8 per 10,000 US civilian population [16]. COPD was also responsible for an estimated 1.5 million emergency room visits, with a resulting age-adjusted rate of 72 visits per 10,000 population [16].

COPD is a leading cause of hospitalization in US adults, particularly in older populations. In 2010, almost 699,000 hospitalizations, were attributed to COPD. The age-adjusted rate of COPD hospitalizations (as the primary cause of hospitalization) was 32.2 per 10,000 population in 2010 [16].

Deaths due to or associated with COPD have not significantly changed since 1999. While the age-adjusted death rate among men declined during 1999–2010 (P = 0.001), the rate among women has not changed significantly (P = 0.127). In 2010, 63, 778 men and 69, 797 women aged ≥ 25 years died of COPD [26]. One of the limitations of using the mortality component of the National Vital Statistics System is that it is based on the underlying cause of death as reported on the death certificate; however, many decedents with COPD listed on the death certificate have their death attributed to another cause [27]. The significance of COPD as a contributor to death is undefined when it is present with diseases more likely to be attributed as the underlying cause of death, such as myocardial infarction or lung cancer [28].

COPD is a very costly disease, with estimated direct medical costs in 2004 of $20.9 billion. The estimated indirect costs related to morbidity (loss of work time and productivity) and premature mortality is an additional $16.3 billion, for a total of $37.2 billion [29]. Because COPD may be present but not listed as the underlying cause of death or the primary reason for hospitalization, these cited estimates may underestimate the true cost of COPD. For example, in another analysis of COPD costs in the US, the total for 2010 was estimated at $32.1 billion [30], but could be up to $100 billion [31] depending on the assumptions surrounding comorbid disease.

Another manifestation of the importance of COPD is its effect on the burden of disease in a population determined using disability-adjusted life-years (DALYs). DALYs for a disease or condition are calculated as the sum of the years of life lost due to premature mortality in the population and the years of life lost due to disability [32]. In 2010, COPD was estimated to be the second leading cause of DALYs lost among the North American population [33]. Worldwide, COPD is expected to move up from being the twelfth leading cause of DALYs lost in 1990 to the fifth leading cause in 2020 [34].

Gender Differences

Smoking-related diseases such as COPD and lung cancer are continuing to increase among women in the United States [35,36], while they have plateaued or are decreasing among men [27,37]. Some evidence has emerged that compared with men at a similar level of tobacco smoking, women may be more likely to develop COPD [38] or that the severity of COPD in women may be increased [39–41].

In the Lung Health Study, which evaluated patients with mild COPD, more women than men demonstrated increased airway responsiveness, although this difference was thought to be related to airway caliber rather than gender [42]. Adult women are more likely to both develop and die of asthma than are men [43–45]. In NHANES III, whereas women reported more physician-diagnosed COPD and asthma than men, men and women had similar rates of decreased lung function, and a similar proportion of both men and women with low lung function had undiagnosed lung disease [3]. The current evidence is inadequate to determine whether women who smoke are more likely to develop COPD or have more severe COPD than men, although this question is being studied by various groups.

Risk Factors and Etiology

Smoking is the dominant risk factor for the development and progression of COPD; however, not all smokers develop COPD, and COPD does occur in persons who have never smoked [1], suggesting that other factors are important in the etiology of COPD. Alpha1-antitrypsin deficiency is an important cause of COPD in a very small percentage of cases [46]. Other undefined genetic factors certainly play an important role in COPD development [38]. The role of infections in both the development and progression of COPD is receiving increased attention, including the role of adenoviral infections in emphysema [47–49].

Occupational and environmental exposures to various pollutants (eg, particulate matter, agricultural dusts) are also important factors in the development of COPD [50,51]. Exposure to indoor air pollutants such as smoke from solid biomass fuels is a major risk factor for COPD especially among women and children in low- and middle-income countries [52,53]. Occupational exposure to fumes and dusts remains an important cause for COPD globally [53,54]. Exposure to outdoor air pollution is associated with a risk of development of COPD as well as exacerbation of the existing disease [53,55].