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* From the Respiratory Pathology Unit (Dr. Sobradillo), Cruces Hospital, Baracaldo (Biscay); the Pneumology Department (Dr. Miravitlles), Hospital General Vall d'Hebron, Barcelona; the Clinical Epidemiology Unit (Dr. Gabriel), Hospital de la Princesa, Madrid; the Pneumology Department (Dr. Jiménez-Ruiz, MD), Hospital de la Princesa, Madrid; the Pneumology Department (Dr. Villasante), Hospital La Paz, Madrid; the Pneumology Unit (Dr. Masa), Hospital San Pedro de Alcántara, Cáceres; the Pneumology Department (Dr. Viejo), Hospital General Yagüe, Burgos; and the Thoracic Surgery Department (Dr. Fernández-Fau), Hospital de la Princesa, Madrid, Spain.
Correspondence to: Victor Sobradillo Peña, MD, Unidad de Patología Respiratoria, Hospital de Cruces, Plaza de Cruces s/n, Baracaldo. Vizcaya 48903, Spain;
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Abstract |
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Design and participants: This is an epidemiologic, multicenter, population-based study conducted in seven areas of Spain. A total of 4,035 men and women (age range, 40 to 69 years) who were randomly selected from a target population of 236,412 subjects participated in the study.
Interventions: Eligible subjects answered the European Commission for Steel and Coal questionnaire. Spirometry was performed, followed by a bronchodilator test when bronchial obstruction was present.
Results: The prevalence of COPD was 9.1% (95% confidence interval [CI], 8.1 to 10.2%), 15% in smokers (95% CI, 12.8 to 17.1%), 12.8% in ex-smokers (95% CI, 10.7 to 14.8%), and 4.1% in nonsmokers (95% CI, 3.3 to 5.1%). The prevalence in men was 14.3% (95% CI, 12.8 to 15.9%) and 3.9% in women (95% CI, 3.1 to 4.8%). Marked differences were observed between sexes in smoking; the percentage of nonsmokers was 23% in men and 76.3% in women (p < 0.0001). The prevalence of COPD varied among the areas, ranging from 4.9% (95% CI, 3.2 to 7.0%) in the area of the lowest prevalence to 18% (95% CI, 14.8 to 21.2%) in the area of the highest. There was no previous diagnosis of COPD in 78.2% of cases (284 of 363). Only 49.3% of patients with severe COPD, 11.8% of patients with moderate COPD, and 10% of patients with mild COPD were receiving some kind of treatment for COPD. Multivariate analysis showed that individuals had a higher probability of having received a previous diagnosis of COPD if they lived in urban areas, were of male gender, were > 60 years old, had higher educational levels, had > 15 pack-year smoking history, or had symptoms of chronic bronchitis.
Conclusions: COPD is a very frequent disease in Spain, and presents significant geographic variations and a very low level of previous diagnosis and treatment, even in the most advanced cases.
Key Words: chronic bronchitis • COPD • epidemiology • prevalence
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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condition or reluctant to consult their physician for respiratory symptoms.13 Consequently, most patients with mild disease do not receive active counseling against tobacco smoking or appropriate pharmacologic treatment. Moreover, some treatments administered to patients with COPD are not adequate for the degree of severity of the disease and do not always follow current guidelines.14 15
Despite the importance of COPD, data on the epidemiology of the disease in population-based studies that include spirometric determinations are scant and even nonexistent in some countries. Furthermore, there is a lack of information on differences in prevalence among different geographic areas of the same or different countries. The IBERPOC study is a population-based epidemiologic study conducted in seven different geographic areas of Spain to ascertain the prevalence of COPD, the prevalence of the different risk factors, and the frequency of previous diagnosis of the condition. Similarly, we assessed the degree of association of the disease with diverse epidemiologic variables, together with the level of diagnosis and existing treatment.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Field Work
Field work was performed from October 1996 to April 1997. A
trained pneumologist was responsible for contacting participants, and
conducted the interviews and pulmonary function tests in each area.
Eligible individuals were randomly selected from the database, which included the 236,412 subjects of the censuses, by software designed specially for the study. A minimum of two unanswered contacts, either by mail or telephone, was required for an individual to be considered a nonresponder. In such cases, the subject was replaced randomly by another of the stratum from the database. Deceased individuals were also replaced. In contrast, subjects with physical or mental handicaps were not replaced. Refusal to participate was considered when an eligible and contacted subject refused to participate on at least two occasions. In this case, the subject was not replaced and was invited to reply to a brief questionnaire by telephone with data on tobacco consumption and the existence of respiratory disease and/or respiratory symptoms.
The European Commission for Steel and Coal questionnaire validated in Spanish was used,16 and information was also collected on smoking habits and socioeconomic level. Along with the questionnaires, the subjects were requested to undergo spirometry, as described below.
Spirometry
Spirometry was performed according to the American Thoracic
Society guidelines,17
with the same type of portable
spirometer (DATOSPIR-200; Sibel S.A; Barcelona, Spain) used in all
seven areas. The predicted values of Roca et al18
were
used. Subjects whose FEV1/FVC value was < 88%
predicted in men or < 89% in women underwent a bronchodilator test
(BDT) with two inhalations of salbutamol, using an inhalation chamber.
The BDT result was considered positive if the difference between
FEV1 or FVC before and after the test was > 200
mL and its relative increase was > 12%.
Diagnostic Criteria of COPD
For the diagnosis of COPD, subjects were required to have no
previous diagnosis of asthma (reply on the European Commission for
Steel and Coal questionnaire) and present the functional obstruction
criteria of the European Respiratory Society (ERS) on
spirometry19
(ie, a
FEV1/FVC ratio in percentage predicted < 88%
in men or < 89% in women). In order to avoid the inclusion of
patients with reversible airway obstruction due to asthma, diagnosis of
COPD was reserved for subjects with negative BDT findings or, in the
case of a positive BDT result, values after the challenge still had to
fulfil the criteria for bronchial obstruction. In the few patients in
whom BDT had not been performed, an absolute
FEV1/FVC value < 81% and
FEV1 < 70% predicted were required for the
diagnosis of COPD, so that possible reversible obstructions that could
pass unnoticed were reasonably avoided. ERS criteria were also followed
for staging COPD severity.19
A subject was considered to be a smoker if he or she consumed at least one cigarette, pipe, or cigar a day, and an ex-smoker if he or she had completely stopped consumption of any type of tobacco for at least the previous 6 months.
Diagnosis of chronic bronchitis was considered when the symptoms of chronic cough with sputum production were present for at least 3 months per year in 2 consecutive years.
Quality Control
The following methods were followed for quality
control: (1) The field work was performed by seven trained
pneumologists with the same equipment in all areas. (2) All seven
investigators underwent a training session prior to the study, which
included a concordance test in the performance of spirometry. Results
of this test have been published previously20
; briefly, an
excellent agreement was found between determinations of FVC,
FEV1, and FEV1/FVC obtained
by all investigators in a wide range of FEV1
values. The intraindividual coefficient of correlation was 4% and
intraclass coefficients of correlation for the investigators were 0.99
for measures of FVC and FEV1 and 0.958 for
FEV1/FVC.20
(3) An independent
observer (MM) reviewed 537 spirometries that corresponded to 11.9% of
those performed. A variation in FVC and
FEV1 > 5% was found in 22 cases, representing
4.1% of the spirometries reviewed. (4) All questionnaires submitted to
the Central Office (Pharma Consult Services S.A.; Barcelona, Spain)
were reviewed by two monitors to filter inconsistencies and missing
data. (5) A review was made of medical records of individuals who
refused to participate but answered the short telephone questionnaire.
Medical records were available for 306 individuals (35% of refusals).
No significant differences were observed between the self-reported
diagnosis of asthma, chronic bronchitis, emphysema or COPD, smoking
habits and respiratory symptoms, and the information registered in
medical records.
Statistical Analysis
The 95% confidence intervals (CIs) for the point estimators of
the prevalence of COPD in the total population, as well as in the
different strata, were calculated. Comparisons between categoric
variables were performed using the point estimators and the 95% CI of
the corresponding odds ratios (ORs). A logistic regression model was
constructed with COPD diagnosis as the dependent variable, and smoking,
social level, age, sex, and place of residence (rural/urban) as
independent variables. Statistical analysis was performed with the SPSS
software for Windows 7.5.2S (SPSS; Chicago, IL).
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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From analysis of the short telephone questionnaires, we observed that persons who declined to participate in the study were somewhat younger (age [SD], 53 [9] years vs 53.4 [8.6] years; p < 0.0001) and more often were men (56.9% vs 49%; p < 0.0001). The number of smokers and ex-smokers (49.5% vs 49.9%; p = not significant) was similar in both groups. The group of refusals presented a lower frequency of previous bronchial asthma diagnosis (1.7% vs 4.9%; p < 0.0001). However, previous diagnosis of chronic bronchitis, emphysema, or COPD was similar in both groups (2.82% vs 4.7%; p = not significant).
Prevalence of COPD
The overall prevalence of COPD and its relationship with tobacco
consumption are shown in Figure 2.
In all, 363 individuals had a diagnosis of COPD. Thus, the prevalence
was 9.11% (363 of 3,981; 95% CI, 8.1 to 10.2%). Functionally, the
majority of COPD diagnoses were based on the presence of chronic
irreversible airflow limitation (74.1% of cases). A BDT result was
positive in 21.7% of COPD patients. In only 15 cases (4.1% of all
cases) was the diagnosis of COPD made without a BDT having been
performed. The prevalence of COPD was 15% (95% CI, 12.8 to 17.1%) in
smokers, 12.8% (95% CI, 10.7 to 14.8%) in ex-smokers, and 4.1%
(95% CI, 3.3 to 5.1%) in nonsmokers. Women presented a prevalence of
3.9% (95% CI, 3.1 to 4.8%) and men were 14.3% (95% CI, 12.8 to
15.9%). The prevalence of COPD rose significantly in the male group as
age and tobacco consumption increased. The prevalence of COPD
regarding smoking habits is presented in Table 2
; odds ratios (ORs) were calculated based on the prevalence in
nonsmokers. In smokers of > 30 pack-years and subjects > 60 years
old, COPD prevalence was 40.3% (95% CI, 34.4 to 46.2%). Very marked
differences existed regarding tobacco consumption between sexes: 76.3%
of women did not smoke vs 23% of men (p < 0.0001). Differences were
also significant when ex-smokers (8.8% vs 40.8%; p < 0.001) and
active smokers (14.9% vs 36.2%; p < 0.001) were compared.
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Among all COPD cases, 23.4% cases (84 of 363) were observed in nonsmokers. The differences were significant: Manlleu and Burgos had the highest percentage of nonsmokers (39% and 36.9%, respectively; p < 0.0001 and p = 0.006 compared with the global) and Caceres, Biscay, and Madrid had the lowest (3.7, 6.2, and 8%, respectively; p = 0.009, p = 0.002, and p = 0.006 compared with the global).
On analyzing the possible explanations for these differences, we found differences concerning tobacco consumption (p < 0.001) among most areas. Manlleu presented the highest figure of nonsmokers and Seville the lowest, while other zones presented similar values. No differences were observed in percentages of ex-smokers (Table 4 ).
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The results of logistic regression analysis that show the variables related to the previous diagnosis of COPD are presented in Table 5 . Tobacco consumption > 15 pack-years, age > 60 years, living in the city, male gender, having a higher educational level (> 12 years vs < 12 years of schooling), and existence of chronic bronchitis and other thoracic diseases had a significant association with the previous diagnosis of COPD, chronic bronchitis, or emphysema. Social class, history of sinusitis, hay fever, lung infection, and industrial occupation did not enter the final logistic model.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In this study, we attempted to avoid possible biases derived from our population sample and the methodology. First, the sample was chosen using a random sample from official censuses of the populations studied, stratified by age groups and sex. Although sampling fractions of the seven areas were different, this should not influence results, since an age- and sex-stratified random sampling proportional allocation was used. In fact, both areas with higher sampling fraction displayed the lowest and the highest prevalences, thus ruling out any systematic bias. Second, the participation rate achieved in the study was very high (69.2% of contact attempts and 81.4% of contacts established), which guarantees the reliability of the results. The third aspect is the possible bias related to nonparticipation. The high number of replies to the short telephone questionnaire (94.6%) permitted us to prove that the prevalences of previously diagnosed COPD, emphysema, or other chronic lung diseases did not differ significantly between participants and refusers. This fact was also confirmed with revision of the clinical histories of some of the refusers.
Diagnostic criteria of COPD usually pose problems in population studies because COPD and chronic airflow limitation, which includes bronchial asthma, may not be differentiated2 4 5 and criteria of airflow obstruction may vary.2 3 4 5 6 7 8 9 10 11 12 In the present study, the criteria used to define COPD excluded patients with a previous diagnosis of bronchial asthma. Furthermore, the functional values used in our study were those indicated by the ERS to define COPD,19 and special attention was paid to the exclusion of subjects with reversible airway obstruction. When it was not possible to perform a BDT, the functional values used to define COPD decreased arbitrarily, so that possible reversible obstructions that might go unnoticed were avoided. The arbitrary values adopted in the study were based on the Intermittent Positive Pressure Breathing Trial,22 which showed the mean value of bronchodilation in COPD to be 5% above the predicted FEV1; thus, with the cutoff values chosen in our study (FEV1/FVC < 81% of predicted and FEV1 < 70% of predicted), it would be very difficult for a subject to be misclassified as COPD in absence of results of a BDT. Our results confirm this hypothesis, since the mean variation over predicted FEV1 after a BDT in our COPD patients was only 2.6%.
Comparison of the prevalences observed in this work with those of other studies is difficult to establish, owing to the use of different criteria for the diagnosis. Variable prevalences have been described in Europe: a British study found results similar to ours, with a prevalence of COPD in the general population of 9.9%9 in those aged 60 to 75 years and 52% of the cases identified had not been previously diagnosed. Lange et al3 in Copenhagen reported a chronic airflow obstruction prevalence of 9.5% in men and 8.6% in women 40 to 59 years old, which doubles the figures found by Bakke et al2 in Norway in this age group using the same predicted values (4.5% in men and 4.8% in women). Differences in prevalence have been observed in studies in other parts of the world.4 5 6 7 8 9 10 11 There are few studies in Spain, and they include small population samples. Marco et al5 studied a sample of 600 men aged 40 to 60 years recruited from the general population and found a prevalence of 6.8%. Brotons et al4 included a similar number of men and women aged 35 to 65 years and established a prevalence of 6.4%, which was higher in men (10.5%) than in women (1.8%).
The unexpected difference found in the prevalence of COPD among the
areas studied is difficult to explain. Although much of this difference
could be attributed to smoking habits, environmental factors, and
diagnostic or coding practices, it may also reflect biological or
genetic differences in the risk of obstructive lung disease.
Differences in smoking habits do seem not to explain most of this
variation, since these differences were small in magnitude and,
moreover, the area with the highest prevalence was the area with the
highest percentage of those who had never smoked. Differences in
prevalence of chronic airway obstruction have been observed in
different ethnicities: a study in Canada showed that ethnic origin made
significant contributions to the estimated risk of airflow obstruction
independent of the effects of age and smoking, with Britons having 3.2
times the risk of East Europeans and 1.9 times the risk of North
Americans for airway obstruction.23
In the study by Samet
et al,24
the prevalence of chronic bronchitis and
emphysema studied by questionnaire was lower in Hispanics than in
Anglo-Saxons, both in men and women. Although Spain is a relatively
small country, some areas have not had significant migratory movements
and their populations are not mixed. In this respect, marked geographic
differences have also been observed in the prevalence of
1-antitrypsin deficiency, which is more
frequent in the north of Spain than in the center and
south.25
The possible influence of genetic factors that
predispose to airway obstruction is reinforced by the results of the
epidemiologic study on bronchial asthma, the results of which showed
that the diagnosis of asthma was as much as three times more frequent
in some regions of Spain than in other regions.26
No clear
geographic gradient (north–south or east–west) in prevalence could be
identified, nor an influence of climate on prevalence.
It is interesting to observe that both areas with the highest prevalences showed an excess of mild cases and of cases detected in women and also had the highest prevalence of cases among patients who had never smoked. This points to other environmental or professional exposures not related to tobacco smoking, together with possible genetic factors, as the cause of the irreversible airway obstruction. The design of the study did not permit investigation of these unexpected differences, although further research has been started to try to find an explanation for these findings.
The probability of having a previous diagnosis of COPD was significantly associated with several factors such as tobacco consumption, age, urban living, and level of studies, suggesting that the intensity of symptoms associated with cumulative smoking, together with greater awareness of the disease and easier access to medical care for those living in urban areas, facilitates the diagnosis of COPD. A study in Spain showed unemployed people to be at 2.06 increased risk of simple chronic bronchitis, due in part to the higher prevalence of smoking, poorer housing, and previous occupational exposures among the unemployed; however, unemployed people consistently reported less frequent contact with specialized practitioners,27 thus explaining in part the lower rate of previous diagnosis among lower socioeconomic levels. Results of the Copenhagen City Heart Study indicate that socioeconomic factors operating from early in life affect the adult risk of developing COPD, independently of smoking.28
In our study, COPD was much more frequent in men. This fact has been observed frequently in studies in Spain4 and France,12 although these differences have not been observed in works in Denmark,3 Norway2 or Sweden.6 Even in the latter study, prevalence of chronic bronchitis was higher in women of all age groups,6 related to a higher prevalence of smoking among women in some Scandinavian countries. The key role of tobacco consumption in the pathogenesis of COPD needs no further comment; however, from our results the increased risk of COPD appears with cumulative consumption of > 15 pack-years in men > 60 years old, or > 30 pack-years in men of all ages, while consumption of < 15 pack-years showed nonsignificant ORs compared with nonsmokers. Comparisons in women are hampered by the small number of smokers or ex-smokers among them.
Only 21.8% of COPD cases found in our study had been diagnosed previously, and only 19.3% of the patients were treated. Furthermore, less than half of our identified severe patients with FEV1 < 50% were receiving any kind of treatment for their respiratory disease. This situation is frequent in other epidemiologic studies in Spain; Marco et al5 found that only 25% of their patients with COPD had had a previous spirometry. In a survey on primary care in Spain, Miravitlles et al15 found that only 47% of patients treated and followed up because of chronic respiratory symptoms had spirometry performed. In the study of Renwick and Connolly,11 63.1% of subjects with COPD received no treatment, even though 70% of those not treated reported respiratory symptoms. Banerjee et al29 found a prevalence of reversible airway obstruction in > 40% of the sample, although only 3% of the patients were treated.
In conclusion, the prevalence of COPD in Spain is high, with marked differences among regions and a low level of previous diagnosis and treatment. These data should stimulate the search for patients with COPD in early stages of the disease and the adoption of more aggressive preventive measures.
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Footnotes |
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The IBERPOC study is an initiative of the workshop "Insuficiencia Respiratoria y Trastornos del Sueño" of the Spanish Society of Pneumology and Thoracic Surgery.
Funding was obtained from Boehringer Ingelheim Spain, SA.
A further important aspect is the lack of knowledge that many patients have of the disease. Patients at an early stage of the disease are either unaware of their
Received for publication November 22, 1999. Accepted for publication May 23, 2000.
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References |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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-1-antitrypsin deficiency: the Spanish experience. Respir Med 92,1181-1187[CrossRef][ISI][Medline]
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