CHAPTER 1
Definition, Epidemiology and Risk Factors

Graham S. Devereux

Division of Applied Health Sciences, University of Aberdeen, Aberdeen, UK

Aberdeen Royal Infirmary, Aberdeen, UK

OVERVIEW

• Chronic obstructive pulmonary disease (COPD) is defined by relatively fixed airflow obstruction.
• The number of individuals diagnosed with COPD is far less than the actual number thought to be affected. Prevalence increases with age and socioeconomic deprivation.
• Globally, COPD is projected to be the third leading cause of death by 2030 with the majority of deaths likely to be in low-/middle-income countries.
• The impact of COPD, particularly exacerbations, on health service resource is considerable.
• Risk factors for COPD include cigarette smoking, indoor air pollution (particularly close and regular exposure to combustion of biomass fuels), outdoor air pollution, occupational exposure to some dusts, vapours, irritants and fumes and a1-antitrypsin deficiency.

Definition

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease characterised by airflow destruction and destruction of the lung parenchyma. The widely used definition put forward by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) is that COPD is 'a common preventable and treatable disease characterised by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lungs to noxious particles or gases. Exacerbations and comorbidities contribute to the overall severity in individual patients'.

COPD is the preferred name for the airflow obstruction associated with the diseases of chronic bronchitis and emphysema (Box 1.1). A number of other conditions are associated with poorly reversible airflow obstruction, for example bronchiectasis and obliterative bronchiolitis. Although these conditions need to be considered in the differential diagnosis of obstructive airways disease, they are not conventionally covered by the definition of COPD. Although asthma is defined by variable airflow obstruction, there is evidence suggesting that the airway remodelling processes associated with asthma can result in irreversible progressive airflow obstruction that fulfils the definition for COPD. Because of the high prevalence of asthma and COPD, these conditions co-exist in a sizeable proportion of individuals and can raise diagnostic uncertainty.

Box 1.1 Definitions of conditions associated with airflow obstruction.

• COPD is a common preventable and treatable disease characterised by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. Exacerbations and co-morbidities contribute to the overall severity in individual patients.
• Chronic bronchitis is defined as the presence of chronic productive cough on most days for 3 months, in each of 2 consecutive years, in a patient whom other causes of productive cough have been excluded.
• Emphysema is defined as abnormal, permanent enlargement of the distal airspaces, distal to the terminal bronchioles, accompanied by destruction of their walls and without obvious fibrosis.
• Asthma is characterised by widespread narrowing of the bronchial airways which changes in severity over short periods of time, either spontaneously or following treatment.

Epidemiology

Prevalence

The prevalence of COPD varies considerably between epidemiological surveys. While this reflects the variation between and within countries, differences in methodology, diagnostic criteria and analytical techniques undoubtedly contribute to disparities among studies. There is no consensus as to the optimal metric of COPD prevalence. The lower estimates of prevalence are usually based on self-reported or 'doctor-confirmed' COPD and are typically 40-50% of the rates derived when spirometry is used. The underdiagnosis of COPD probably arises because many individuals fail to recognise the significance of symptoms and present relatively late with moderate or severe airflow obstruction (Figures 1.1-1.3).

Figure 1.1 Known cases of COPD may represent only the 'tip of the iceberg' with many cases currently undiagnosed.

Figure 1.2 Lifetime prevalence of diagnosed COPD in males and females (per 1000) resident in England 2001-2005.

Figure adapted from Simpson CR, Hippisley-Cox J, Sheikh A. Trends in the epidemiology of chronic obstructive pulmonary disease in England: a national study of 51 804 patients. British Journal of General Practice 2010; 60(576): 277-284.

Figure 1.3 Prevalence (per 1000) of diagnosed COPD in UK men (?) and women (?) grouped by age, between 1990 and 1997.

Reproduced from Soriano JB, Maier WC, Egger P et al. Thorax 2000; 55: 789-794, with permission of BMJ Publishing Group.

Globally, the World Health Organization (WHO) estimates that 65 million people have moderate to severe COPD. In the UK, a national study reported that 10% of males and 11% of females aged 16-65 had an abnormally low FEV1. Similarly, in Manchester, non-reversible airflow obstruction was present in 11% of subjects aged >45 years, of whom 65% had not been diagnosed with COPD. In the UK, an estimated 3 million individuals have COPD but only 1.2 million have a formal diagnosis. In the US, an estimated 24 million have evidence of impaired lung function consistent with COPD, while 12.7 million US adults have diagnosed disease. In a study of 12 countries in Europe, North America, China, Australia, South Africa and the Philippines, the prevalence of COPD in those over the age of 40 years based on lung function criteria was 10.1%, being more common in males (11.8%) than females (8.5%). The prevalence of COPD increases with age, almost doubling with each decade from the age of 40 years. In the UK, the lifetime prevalence of diagnosed COPD has been reported to be increasing and is more common in males than females. In contrast, in the US the prevalence of COPD has been reported to be stable, with the disease being more common in females. COPD is associated with socioeconomic deprivation. In a systematic review, individuals from the lowest socioeconomic strata were at least twice as likely to have COPD when compared with more affluent individuals, regardless of the population studied, metric of socioeconomic status or COPD outcome investigated (Figures 1.4, 1.5).

Figure 1.4 Prevalence of COPD confirmed by spirometry in a Finnish National Survey: association with metrics of socioeconomic status.

Figure derived using data from Kanervisto M et al. Low socioeconomic status is associated with chronic obstructive airway diseases. Respiratory Medicine 2011; 105: 1140-1146.

Figure 1.5 Prevalence of diagnosed COPD in UK men and women (per 1000) between 1990 and 1997.

Reproduced from Soriano JB, Maier WC, Egger P et al. Thorax 2000; 55: 789-794, with permission of BMJ Publishing Group.

Mortality

Globally, COPD was ranked sixth as the cause of death in 1990, but with the ageing of the world population, the epidemic of cigarette smoking in developing countries and reduced mortality from other currently common causes of death (e.g. ischaemic heart disease and infectious diseases), it is expected that COPD will become the third leading cause of death worldwide by 2030. In 2012, an estimated 6% (3 million) of deaths worldwide were attributed to COPD, and more than 90% of these occurred in low- and middle-income countries. In the UK in 2014, there were approximately 30 000 deaths attributed to COPD, with 15 300 of these deaths in males and 14 700 in females. These figures suggest that in the UK, COPD underlies 5.3% of all deaths, 5.5% of male deaths and 5.0% of female deaths. In the US, the most recent data, covering 1999-2013, indicate that 136 000 (5.5%) deaths are a consequence of COPD, and that it is the third leading cause of death behind cancer and heart disease.

In the UK, over the last 40 years, mortality rates due to COPD have fallen in males and risen in females. In the US, the age-adjusted death rate for COPD in males is approximately 1.3 times greater than the rate in females. However, since there are more females in the general US population than males, the actual number of females dying from COPD has exceeded the number of males dying since about 1999. COPD mortality rates increase with age, disease severity and socioeconomic disadvantage. On average, in the UK COPD reduces life expectancy by 1.8 years (76.5 versus 78.3 years for controls). Mild disease reduces life expectancy by 1.1 years, moderate disease by 1.7 years and severe disease by 4.1 years. In the US, it has been estimated that a male smoker at the age of 65 years will have his life expectancy reduced by 0.3, 2.2 and 5.8 years, with mild, moderate and severe disease respectively. For a female smoker at age 65, mild, moderate and severe COPD is...