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(Chest. 2000;117:326S-331S.)
© 2000 American College of Chest Physicians

Scope of the COPD Problem in North America*

Early Studies of Prevalence and NHANES III Data: Basis for Early Identification and Intervention

Thomas L. Petty, MD, Master FCCP

* From the University of Colorado Health Sciences Center, Denver, CO.

Correspondence to: Thomas L. Petty, MD, Master FCCP, University of Colorado Health Sciences Center, 1850 High St, Denver, CO; e-mail: tlpdoc{at}aol.com


   Abstract
TOP
 Abstract
Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
 Discussion
 Summary
 References
 
COPD is a common disease that is often not diagnosed in the primary-care setting. This review highlights the findings of studies ranging from the early 1960s to the third National Health and Nutrition Examination Survey (NHANES III) study, undertaken to try and accurately estimate the prevalence of COPD in the US population. Results of the NHANES III indicate that COPD remains frequently underdiagnosed, and that spirometry should be more widely used in the primary-care setting to identify asymptomatic disease. Early intervention, in particular smoking cessation, could alter the course and outcome of disease in patients with COPD.

Key Words: COPD • identification • National Health and Nutrition Examination Survey III • prevalence


   Introduction
TOP
 Abstract
 Introduction
Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
 Discussion
 Summary
 References
 
It has been estimated that as many as 16 million Americans have symptomatic COPD,1 a disease that is now the fourth most common cause of death in the United States, and accounted for > 106,000 deaths in 1996.2 COPD is the only major disease among the top 10 causes of death that is continuing to increase in both prevalence and mortality3 ; in 1993, physicians visits, hospitalizations, and consumption of other health-care resources for COPD cost approximately $15 billion.4 In view of the alarming statistics, it is important to understand the scope of the problem as it exists in North America now, and to compare earlier studies of North American populations with contemporary data on prevalence. The purpose of this article, therefore, is to give a historical perspective on COPD prevalence, and to present the most recent information on prevalence available from a large population sample.


   Earlier Prevalence Studies
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
National Health and Nutrition...
 The Lung Health Study
 Discussion
 Summary
 References
 
Early regional COPD prevalence studies included Berlin, NH5 ; Tecumseh, MI6 ; and Glenwood Springs, CO.7 These studies surveyed subjects with somewhat different degrees of airflow obstruction and used dissimilar definitions of COPD. In all studies, an attempt was made to separate COPD from acute intermittent and/or reversible asthma.

In Berlin, NH, the prevalence of a broad designation, chronic nonspecific respiratory diseases, ranged from 15.4 to 39.1% in men, in different locations in the community where occupational risk factors could have been relevant.5 In women, the prevalence of chronic nonspecific respiratory diseases ranged from 15.2 to 20.9%. The prevalence of irreversible obstructive disease, which refers to COPD, ranged from 3.1 to 21.7% in men, and 6.2 to 13.9% in women. In this study, a FEV1 < 60% predicted was considered abnormal.

In Tecumseh, MI, in a study of > 9,000 men and women of all ages, abnormality of FEV1 was arbitrarily set at < 65% predicted, with an accompanying FEV1/FVC ratio of < 80%.6 There were no air pollution or occupational risk factors in Tecumseh, and approximately 14% of adult men and 8% of adult women had chronic bronchitis, obstructive airways disease, or both.6

In Glenwood Springs, CO, a nonindustrial, non–air-polluted city at an altitude of 5,300 feet, a random sample of 20% of the adult population between the ages of 20 and 69 years (2,905 people) resulted in the testing of 287 men (96.5% of those randomly selected) and 328 women (96.0% of those randomly selected) in 1967.7 The definition of abnormality was an FEV1/FVC ratio < 60% in the presence of dyspnea, cough, expectoration, or wheeze. Using this definition, 17% of the men had chronic bronchitis, 13% had COPD (ie, spirometric abnormalities), and 2% had asthma. In women, 10% had chronic bronchitis, 4% had COPD, and 1% had asthma. Twenty-seven percent of men and 13% of women had any type of abnormality that could be symptoms, spirometric abnormalities, or both. Chronic bronchitis and COPD were related to smoking and age in both sexes.

The Glenwood Springs study was important because a follow-up of the original abnormal population and a random sample of an equal number of normal subjects was conducted 6 or 7 years following the original prevalence study.8 In the follow-up, subjects found to have spirometric abnormalities in the earlier study demonstrated progression of these abnormalities 6 or 7 years later. In contrast, patients who had symptoms but no spirometric abnormalities maintained normal spirometry findings throughout the follow-up. It was found that spirometric abnormalities were more significant in predicting decline of pulmonary function and death, which was higher in the abnormal population (ie, 14 vs 6 in normal population; p = 0.01). This is consistent with a more extensive study that related the relevance of decline of airflow, but not of mucus hypersecretion, to mortality from chronic lung disease.9 In a later follow-up, 11 years after the first study, there were 21 deaths from 117 abnormal subjects, compared with only 8 deaths from 116 originally normal subjects (p = 0.01). All of the respiratory deaths were from the originally abnormal population.10


   National Health and Nutrition Examination Survey III
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
The Lung Health Study
 Discussion
 Summary
 References
 
A recent analysis of data from the third National Health and Nutrition Examination Survey (NHANES III) documents the contemporary prevalence of obstructive lung disease (OLD) in large population samples.11 Full details of this study are beyond the scope of this presentation and have previously been reported11 ; however, there are a number of important findings that should be highlighted. Briefly, this study was limited to adults aged >= 17 years, who classified themselves as white or black, had spirometric testing performed, and completed an extensive respiratory questionnaire concerning symptoms and smoking status. Following exclusions, 16,084 patients were available for analysis. Ever-smokers were defined as smoking > 100 cigarettes. A history of cigar and pipe smoking was obtained, and was analyzed for men. There were too few women pipe or cigar smokers, however, for prevalence data to be accurate. Subjects were asked about the previous diagnosis of chronic lung disease and details about their current symptoms. Spirometry was done based on the American Thoracic Society recommendations.12 In NHANES III, spirometric abnormalities were judged to be present if the FEV1/FVC ratio was < 0.70. From this study, it was possible to further divide this group into subjects with FEV1 >= 50% predicted, or < 50% predicted, corresponding to people with stage I vs stage II/III OLD.13

The final data set, 16,084 subjects, represents an estimated 169.3 million adults in the United States. The tabular results of all patients listed in the NHANES III are presented in the original publication with four Figures reproduced from this initial report.11 Figure 1 presents the age-specific percentage of patients stratified by race and sex, with current or past OLD, and shows no clear relationship between age and reported disease. Figure 2 presents the age-adjusted percentage of the population with an FEV1/FVC ratio < 0.70 and no current diagnosis. These data show a significant prevalence of OLD in white male former smokers, never-smokers, and current smokers. Black female never-smokers, black male current smokers, and black male pipe or cigar smokers also have a significant prevalence of OLD; white female current and former smokers also have a high prevalence of OLD. These data show a variation by sex, race, age, and smoking status, with a proportion of the population with low lung function being higher among men, whites, and current or former smokers. Figure 3 is the age-adjusted percentage of patients stratified by race, sex, and smoking status with an FEV1/FVC ratio < 0.70 and an FEV1 percent predicted >= 50% or < 50% of the expected value. Over 71.7% of the population with a low level of lung function, as indicated by an FEV1/FVC ratio < 0.70, did not have a current diagnosis of OLD. Even among subjects with moderate to severe pulmonary impairment, as indicated by an FEV1 < 50% predicted, 46.2% did not have a current diagnosis of OLD. Across sex, race, and smoking categories, this proportion ranged from 59 to 88% (Fig 4 ). People with a past diagnosis of OLD accounted for a small proportion of this group, subjects without a current diagnosis (Fig 4) .



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  		Figure 1. Age-specific percentage of population with OLD.

 


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  		Figure 2. Age-adjusted percentage of population with FEV1/FVC < 0.70 and no current diagnosis of OLD.

 


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  		Figure 3. Age-adjusted percentage of population with FEV1/FVC < 0.70.

 


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  		Figure 4. Age-specific percentage of population with FEV1/FVC < 0.70.

 

   The Lung Health Study
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
Discussion
 Summary
 References
 
The Lung Health Study showed that stopping smoking can greatly retard the rate of decline in FEV1 compared to continuing to smoke in a population aged 35 to 60 years. This landmark study forms an additional foundation for the early history of smoking in order to identify abnormality and risk of progressive impairment on the pathway to symptomatic COPD.14 Unfortunately, only a small percentage of subjects were able to stop smoking for the full 5 years of this study; only 22% who received special care and 5% who received usual care were able to quit and stay abstinent. This study was done at a time when the only form of nicotine replacement was nicotine-containing chewing gum. Subsequently, the nicotine patch, spray, and inhaler have added to the armamentarium for nicotine replacement. Bupropion has recently been shown to be superior to the nicotine patch,15 16 and combining the two approaches has achieved the highest rate of success thus far, approaching 36% at 1 year.16 Thus, there are now newer therapeutic strategies to offer the smoker who is beginning to develop airflow obstruction.


   Discussion
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
 Discussion
Summary
 References
 
Early prevalence studies showed that COPD was common and related to smoking in various industrial and nonindustrial communities in the United States. Smoking was more prevalent in the 1960s and 1970s than in the period of the NHANES III study. For example, between 1983 and 1995, overall smoking prevalence among those aged >= 18 years declined from 34 to 26% for white men, from 41 to 29% for African-American men, from 30 to 24% among white women, and from 32 to 23% among African-American women.2 The primary message of the NHANES III is that chronic OLDs, most commonly COPD, are greatly underdiagnosed in the present era in the US population. It is important to note that most of the underdiagnosis occurs in patients with mild to moderate disease; if these patients can be identified in early and asymptomatic stages of disease, interventions such as smoking cessation and other therapies to reduce inflammation can be expected to alter the course and prognosis of disease.

Without a doubt, smoking cessation is the most important approach to management in all OLD. Smoking cessation is most likely to be beneficial when it is accomplished at an early age with only mild evidence of airflow obstruction, as judged by simple spirometry. Most of the subjects in the NHANES III with evidence of airflow obstruction in spirometric testing never had a diagnosis of asthma, chronic bronchitis, emphysema, or COPD, in spite of the fact that > 56% of subjects reported that they had at least one respiratory symptom. Significant OLD was found in nonsmokers, suggesting undiagnosed asthma, or that COPD may be more common in nonsmokers than expected.

The results of the NHANES III confirmed previously known associations between aging and increased airway obstruction.17 Mild airways obstruction (FEV1 > 50% predicted) increases with age (Fig 2) , while the current diagnosis of OLD did not show a clear-cut pattern with increasing age (Fig 4) . It is known that individuals with low lung function tend to die young.9 17 18 These data also suggest that patients > 45 years old may have significantly decreased lung function that remains undiagnosed (Fig 2 , 4) .

The NHANES III study of OLD included patients with asthma, chronic bronchitis, and emphysema. Subjects with all three disease categories had significant respiratory symptoms and low levels of lung function. Inadequate treatment of chronic asthma may lead to chronic irreversible airflow obstruction, and this can be a component of the spectrum of COPD.19 Chronic asthma is a potentially reversible disease when diagnosed early and treated with the systemic and strategic use of bronchoactive and anti-inflammatory medications.20 Preventing or forestalling the burden of COPD may be possible through aggressive smoking cessation and perhaps medication, which may reduce the inflammation of conducting airways of the lung and surrounding alveolar attachments.

The NHANES III survey is subject to several limitations. Selection was biased in that it was limited to a noninstitutionalized, nonmilitary population, so the selection was not truly a randomized general population. Only patients who were ambulatory and able to participate were studied. In addition, the entire medical history, including the previous and current diagnosis, the respiratory symptoms, and the smoking habits, were self-reported, possibly introducing a level of inaccuracy. Another potential bias of this study design is that not everyone completed pulmonary function testing. It is possible that subjects unable to undertake lung function testing were also more likely to have low levels of lung function, thus resulting in an underestimate of the prevalence of OLD in the United States. The use of objective spirometric data to identify OLD mitigates these weaknesses.

Spirometric testing may provide an opportunity for intervention in the United States and elsewhere. Since early intervention through smoking cessation may alter the course and prognosis of COPD, it is important that all clinicians who encounter respiratory symptoms in a smoker are able to make an accurate diagnosis. Previous studies have shown that symptoms and signs alone are not adequate to be able to diagnose COPD.21 22 Accordingly, spirometry, like BP or cholesterol measurements, must be widely applied for the assessment and intervention of patients with undiagnosed OLDs.

The suggestion that physicians need to focus on smokers who are vulnerable to the damaging effects of tobacco smoke was made nearly 25 years ago.23 Although the nitrogen washout test (closing volume) to assess small airways damage was in vogue at that time, it was astutely recognized that a simple spirometric test should be used in widespread clinical testing. The mid-maximum expiratory flow rate was offered as such a test, and it was advised for insurance examinations and in routine physical examinations of smokers at risk.23 Subsequently, the value of the FEV1 and FEV1/FVC ratio in predicting a rapid decline in FEV1 over time became established,24 and shortly thereafter a plea was made for spirometric testing as a routine in primary-care physicians’ offices so that COPD could be diagnosed in its early, incipient stages.25 The need for new, simple devices suitable for the office use has been stressed.

A disease state cannot be treated unless it is diagnosed. The widespread use of spirometry is fundamental to diagnosis and treatment of OLD. Determining what impact modern-day treatment may have in the course and prognosis of all stages of OLD identified in NHANES III will require prospective clinical trials.

A new national health-care initiative is aimed at involving primary-care physicians in the early diagnosis and treatment of OLDs.4 26 The National Lung Health Education Program is promoting the widespread use of simple spirometry to measure FEV1, FVC, and the FEV1/FVC ratio. Data from this study show that the FEV1/FVC ratio is a sensitive indicator of the presence of COPD. Simple, hand-held, accurate, and reliable spirometers are currently available for use in the primary-care physician’s office and clinic, as well as in the workplace. Hopefully, the widespread use of spirometry by both primary and specialty physicians may ultimately identify millions of persons with undiagnosed early COPD who are amenable to early interventional therapy.


   Summary
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
 Discussion
 Summary
References
 
COPD has been known for many years to be a disease of high prevalence, both in industrialized and in nonindustrialized communities. Identification of patients with COPD-related symptoms and spirometric abnormalities identifies a population at risk for premature morbidity and mortality from both respiratory and nonrespiratory causes. The recent NHANES III population analysis sheds additional light on the high prevalence of OLDs, of which COPD is a major component. Since the majority of patients both with respiratory symptoms and spirometric abnormalities have never had their conditions diagnosed, nor are they receiving systematic therapy, it is imperative at this time to promote the widespread search for patients with mild and moderate forms of disease, even before they are symptomatic. Identification of smokers who are prematurely losing ventilatory function will improve the rate of decline of ventilatory function, as judged by FEV1. New therapies useful in smoking cessation may improve the rate of cessation dramatically. Thus, together, spirometric tests of smokers and symptomatic patients to identify abnormalities, the use of a growing number of smoking cessation strategies, and the possibility of other anti-inflammatory drugs to stem the rate of decline, offer a new approach for changing the course and outcome of COPD.


   Footnotes
 
Abbreviations: NHANES III = third National Health and Nutrition Examination Survey; OLD = obstructive lung disease


   References
TOP
 Abstract
 Introduction
 Earlier Prevalence Studies
 National Health and Nutrition...
 The Lung Health Study
 Discussion
 Summary
 References
 

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