In the subpopulation of participants aged > 50 years, the prevalence of current asthma was 5.1%, the prevalence of current chronic bronchitis was 5.8%, and the prevalence of ever having had emphysema was 5.0% in the US NHANES III survey. In the UK GPRD subpopulation of participants aged > 50 years, the prevalence of current asthma was 1.6%, the prevalence of current chronic bronchitis was 1.1%, and the prevalence of current emphysema was 1.1% (data not shown). The seven mutually exclusive disease groups of this proportional Venn diagram also can be displayed as stacked bars, for comparison by gender and age (Fig 3). The relative size of the asthma-only group decreased with increasing age, both in women and men in the United States and the United Kingdom. In the NHANES III data, probably because acute bronchitis could have been misclassified as chronic bronchitis in some cases via the self-reported questionnaire, combinations of chronic bronchitis with asthma or chronic bronchitis alone appeared at very young ages. Emphysema was reported consistently from age 50 years onward. Combinations of two of the three OLD conditions occurred among 21.2%, 31.4%, and 14.4%, in those patients in the age groups of 60 to 69 years, 70 to 79 years, and > 80 years, respectively.
By contrast, in the UK GPRD, emphysema and chronic bronchitis are virtually nonexistent diagnoses before 50 years of age. After age 50 years, the frequent diagnoses of chronic bronchitis and emphysema together as COPD gave little room for chronic bronchitis-only or emphysema-only diagnoses. Therefore, combinations of two of the three OLD conditions occurred among 41.5%, 58.8%, and 65.5% of patients in the age groups of 60 to 69 years, 70 to 79 years, and > 80 years, respectively.
Finally, according to the spirometry data of NHANES III, US OLD participants with chronic bronchitis or emphysema, with or without a concomitant diagnosis of asthma, differed widely regarding the prevalence of airflow obstruction among patients with a diagnosis of emphysema only, with only 37.4% of patients having airflow obstruction confirmed by spirometry. The prevalence of airflow obstruction was significantly higher among participants with combinations of emphysema and chronic bronchitis (57.7%), with emphysema and asthma (51.9%), and with all three OLD diseases concomitantly (52.0%). Among all NHANES III participants with airflow obstruction, accounting for 4.8% of the general population, 58.3% reported no diagnosis of any of the three OLD conditions (Fig 4). The patterns of airflow obstruction prevalence were confirmed when the analysis was restricted to participants aged > 50 years (Fig 5). The prevalence of airflow obstruction in the seven mutually exclusive areas were as follows: asthma only, 26.5%; chronic bronchitis only, 29.6%; emphysema only, 45.5%; asthma plus chronic bronchitis, 55.8%; asthma plus emphysema, 48.7%; chronic bronchitis plus emphysema, 59.7%; and asthma plus chronic bronchitis plus emphysema, 49.0%. Still, 9.3% of the NHANES III population who were > 50 years of age had objective airflow obstruction without any respiratory diagnoses.