Chronic obstructive pulmonary disease (COPD) is a rising cause of morbidity and mortality worldwide,1,2 and Portugal is no exception.3

In 1990 COPD was the sixth most common cause of death worldwide and was ranked 12th for DALYs (disability-adjusted life years).4,5 It has been projected that by 2020 it will have risen to 5th rank, and be the third most common cause of death.5–7

This situation has led to the development of the Global Initiative for COPD (GOLD)7 of which the primary goal is to control and invert the burden of COPD.

The two studies had different methodology.

In Table 1, sociodemographic characteristics of study samples for both studies are described. In the Pneumobil, out of 9061 individuals included, 62.8% were male, 13.3% were smokers and 63.6% were never smokers. In the 2002 Study, from the 1384 individuals included, 49.5% were male, 25.4% were smokers and 52.7% were never smokers.

As shown in Fig. 1 and in Fig. 2, there was an overall COPD prevalence of 8.96% in the Pneumobil studied population (age range 40 years old), 11.9% in males and 5.9% in females. In the 2002 Study, 5.34% of COPD cases were identified (age range 35–69 years old), 6.3% in males and 4.5% in females.

Figure 1.

Distribution of Pneumobil COPD cases, by age and gender (post-BD criterion).

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Figure 2.

Distribution of 2002 Study COPD cases, by age and gender (pre-BD criterion).

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In these two figures, the distribution of COPD cases by age and gender was also shown. More than 61% of cases were identified above 60 years old in Pneumobil Study vs. more than 32% in 2002 Study. Moreover, 26.5% of cases were identified above 70 years old in Pneumobil Study, an age range not studied in 2002. It should also be noted, that below 60 years old, a higher proportion of cases were females in the 2002 Study vs. Pneumobil (29.8% vs. 10.8%).

Regarding smoking habits for COPD cases found in both studies, in Pneumobil the prevalence in smokers was 15.4% and in never smokers it was 6.7%. In the 2002 Study the prevalence in smokers was 8.8% and in never smokers was 4.4%.

Figs. 3 and 4 show the distribution of COPD severity (GOLD in Pneumobil Study and adapted from GOLD in 2002 Study). In both studies, it can be seen that the proportion of the combination of stage I and II are similar, 83.9% in Pneumobil Study and 87.8% in 2002 Study. However, more cases were found in stage I in 2002 Study (47.3% vs. 30.8%). In addition, even with a cut-off of 69 years old in the 2002 Study, the proportion of combined stage III and IV is very similar in both studies, but higher in Pneumobil (16,1% vs. 12,2%).

Figure 3.

Distribution of COPD cases by GOLD stages in Pneumobil (post-BD).

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Figure 4.

Distribution of COPD cases by adapted severity stages in the 2002 Study (pre-BD).

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In Table 2 we present the distribution of COPD cases by smoking status and severity. In Pneumobil 21.2% of cases were found in smokers and in 2002 Study it doubled to 41.9%. As referred to above, there was a low prevalence of smokers in Pneumobil (13.3%) compared to 25.4% in the 2002 Study.

In general, the distribution of the cases by smoking status and severity (Table 2) overlaps the general distribution of severity in both studies (Figs. 3 and 4), with around 85–90% of cases in stage I and II. In more severe stages, the trend is similar in both studies by smoking class, but for instance, in stage III the ex-smokers in 2002 are 9.1% of cases, while in Pneumobil we found 18.2% (Table 2).

The different age range and the higher fraction of ex-smokers in Pneumobil are possible reasons to account for these findings.

Three major and important limitations are present in these studies: (1) for Pneumobil, it is not a truly randomized study; (2) for 2002 Study, the criterion for COPD was not based on a post-bronchodilator spirometry; (3) criteria for obstruction is different in the two studies so the prevalence results cannot be compared. Nevertheless, some results are valid on their own.

Different figures for COPD prevalence were found in the two studies and diverse methodologies may explain these different values. In Pneumobil the age range was larger with individuals over 70 years being included. Even if the fixed ratio criteria for obstruction may overestimate the prevalence in this age range, it is possibly more real than the prevalence of the 2002 Study that excluded individuals of 70 and over. The COPD prevalence of the 2002 Study may be appropriate for the age range studied, but it is surely an underestimate for the general population.

The concern that older people could be missed because they might not come to centres (possible reason for the low overall prevalence in participants of 70 years and over in Pneumobil Study), was accounted for in the design of the 2002 Study that excluded this age range, but did not translate into significant different degrees of severity. Nevertheless, more severe stages of disease were found in Pneumobil (perhaps more severe cases volunteered to undergo testing) and this may have under-estimated the prevalence of COPD in 2002.

A different time frame is another reason for differences. The known prevalence of smoking habits in Portugal was not different in 1995 vs. 2002 (total 17.3% vs. 18.0%), except for a slight increase in female smokers (6.5% vs. 7.9%).23

The lack of randomization is a possible reason for the low prevalence of smokers and ex-smokers in Pneumobil Study.

The occurrence of more female cases at younger ages in 2002 Study is in line with this time frame difference.

Although the participation rate of the 2002 Study was very low, the representative and random selection procedure of the included sample was assured, which is an added value for this study.

The fact that Pneumobil was not a truly randomized study, as individuals volunteered for the survey, is a possible factor for discrepancies between the two studies (people living far away from the collection sites might have been excluded). But in a sample of 12,684 individuals this bias would have been minimized and the bringing of the vehicle to people, who were worried about having the disease, may explain more severe COPD cases reached.

As a protocol option, in the 2002 Study no bronchodilator was administered to test reversibility, mainly for ethical and operational reasons. This was also a limitation of many other surveys at that time, like NHANES III.24

Although it was not possible to apply a true GOLD criteria (due to absence of reversibility test, which might overestimate COPD cases) data can be reasonably accepted, since most of asthma and other chronic airflow limitations were excluded by the questionnaire. This was also the opinion of Fukuchi et al.25 in a Japanese prevalence study.

Another important aspect is that the two studies were done with two different spirometers. If for the Pneumobil Study we think that there is no reason for suspecting errors, for the 2002 Study it may not be the case. A possible limitation of the FVC value (software cutting values of low flows) is suspected because the median of FEV1/FVC ratio was higher than expected (84.4%). So, the prevalence rate estimated using fixed ratio criteria can, in fact, be underestimated in 2002 Study.

Consistent with others,8,21,26 these studies also showed higher prevalence rates in men. Increasing age is a significant factor related to prevalence and the older population appears to have an increased risk for COPD, independent of their smoking history.

Globally, the most important risk factors associated with COPD in these studies were age over 60 years, male gender and smoking exposure.

Nevertheless, the presence of a significant proportion of COPD cases in never smokers may indicate that other risk factors may be present in the Portuguese population (e.g. biomass exposure, previous respiratory diseases, childhood infections).

Higher COPD prevalence values are expected in future prevalence studies as the major limitations of the two studies, that accounted for underestimation (age range, randomization, adequate spirometers, use of post-BD spirometry), should be corrected.

These two studies contributed to our knowledge of COPD prevalence in Portugal, as they suggest a somewhat lower frequency of occurrence than in other European countries. This can be accepted as the consequence of lower percentage of smoking people and of smoking history.

Globally, the most important risk factors associated with COPD were age over 60 years, male gender and smoking exposure.

In these surveys, COPD severity stages I and II accounted for over 85% of the cases, and this fact indicates the need for special attention to spirometric approach, its quality and its abnormalities.

However more frequent in smokers and ex-smokers, COPD occurred also frequently in non-smoker men and women, and this fact justifies a closer attention to other causal factors in the future.

All aspects and limitations regarding methodology highlight the need for a standardized method to evaluate COPD prevalence and associated risks factors, so that results can be compared across countries, as is the case with BOLD project.15

It is believed that a concerted effort by everyone involved in health care, governments, public health officials, health care workers, and even the general public, is needed to control this still major public health problem.7

Both studies were conducted by the Respiratory Portuguese Society and funded by Boehringer Ingelheim and Pfizer.

The authors have no conflicts of interest to declare.