What are the prevalence, incidence, relative risk, attributable risk, and population attributable risk of Chronic Obstructive Pulmonary Disease (COPD) in smokers and non-smokers, particularly in adults aged 50-70 with a significant smoking history?

COPD Epidemiology in Smoking and Non-Smoking Populations

Prevalence

In the United States, COPD prevalence is substantially higher among smokers compared to never-smokers: current smokers demonstrate a weighted prevalence of 12.6%, ex-smokers 9.6%, and never-smokers 4.1%. 1

• Among general practice patients aged 40-70 years who are current smokers with ≥15 pack-years, the prevalence of COPD reaches 46.6%, with approximately two-thirds of these cases being previously undiagnosed 2
• In the broader US adult population aged 25-75 years, mild COPD (FEV1/FVC <0.7, FEV1 ≥80% predicted) has an estimated prevalence of 6.9%, while moderate COPD (FEV1/FVC <0.7, FEV1 <80% predicted) affects 6.6% 3
• Never-smoker COPD accounts for 25-50% of all COPD cases globally, representing a substantial disease burden despite lower individual risk 1
• In African populations, the pooled data shows smoking as a significant risk factor with an odds ratio of 2.80 (95% CI 2.19-3.59) 3

Incidence and Natural History

The often-cited statistic that only 15-20% of smokers develop clinically significant COPD likely underestimates the true burden, as COPD often has its roots decades before symptom onset. 3

• From 1999 to 2018, COPD prevalence among current smokers increased from 13.7% to 21.9%, remained stable at approximately 10.1% among ex-smokers, and declined from 4.9% to 3.3% among never-smokers 1
• The disease follows a variable natural history, with impaired lung function growth during childhood and adolescence leading to lower maximally attained lung function in early adulthood, particularly in teenage smokers 3

Relative Risk

Current smokers face the highest mortality risk, with a hazard ratio of 1.894 (95% CI 1.386-2.590) compared to non-smokers with COPD, while former smokers have an intermediate risk with HR 1.619 (95% CI 1.198-2.188). 4

• In African populations, previous pulmonary tuberculosis carries the highest odds ratio of 5.98 (95% CI 4.18-8.56), followed by smoking with OR 2.80 (95% CI 2.19-3.59), and biomass fuel use with OR 1.52 (95% CI 1.39-1.67) 3
• Among Spanish smokers and ex-smokers over 40 years of age, COPD prevalence was 16.4% (95% CI 12.9-19.9), with age and cumulative pack-years being the most significant risk factors 5
• Never-smokers with COPD demonstrate less severe disease with milder airflow limitation and lower systemic inflammation burden compared to smokers 6, 7

Attributable Risk

Age and cumulative tobacco consumption (pack-years) are the two major attributable risk factors for COPD development in smokers. 5

• In never-smokers, the most important attributable risk factors include: biomass smoke exposure (68.06%), long-standing asthma (37.50%), childhood lower respiratory tract infections (32.60%), and outdoor air pollution exposure (17.92%) 8
• Occupational exposures to organic and inorganic dusts, chemical agents, and fumes represent underappreciated but significant attributable risk factors in never-smoker COPD 6
• Female gender, older age, and lower income are independent risk factors across all smoking categories 1

Population Attributable Risk

COPD is the fourth-leading cause of death in the United States, with mortality rates of 21.1% among current smokers with COPD, 29% among ex-smokers with COPD, and 12% among never-smokers with COPD. 1, 3

• Approximately 35% of deaths in patients with moderate to severe COPD are directly attributable to COPD itself, while 26% are due to cardiovascular causes and 21% due to cancer 7, 9
• The proportion of current smokers in the US general population has declined from 1999 to 2018, while never-smokers have increased, yet the absolute burden of COPD among current smokers continues to rise 1
• Marital status significantly modifies the smoking-mortality relationship, with single/never married former smokers exhibiting the highest mortality risk (HR 3.711,95% CI 1.130-12.187) 4

Clinical Implications

Post-bronchodilator spirometry showing FEV1/FVC <0.70 is mandatory for diagnosis in all patients regardless of smoking status. 7, 9

• Never-smokers with COPD present at younger ages (mean 53.90 ± 8.77 years) compared to smokers (59.29 ± 10.28 years), with female predominance (70% vs 25%) in the never-smoker group 8
• At presentation, never-smokers typically have GOLD Grade II severity, while smokers more commonly present with GOLD Grade III 8
• Underdiagnosis is particularly common in younger age categories (40-59 years) among current smokers, emphasizing the need for active case-finding in primary care 2