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COPD prevalence

Systematic review
Results
Comment

How many people have chronic obstructive pulmonary disease? A deceptively simple question, this, according to a systematic review of prevalence rates [1]. It concludes that we just don’t know, but it is probably more than we think.

The problems are the ones that any of us would think of, namely the definition of the population in which we are interested, the definition of what COPD is, and how COPD is measured. What we seem to have is a number of goalposts all moving randomly in different directions .

Systematic review

The review used a single MEDLINE search designed to detect any studies that might have quantified the prevalence of COPD in countries or regions. Studies of interest were those that had a total population estimate or sex or age specific estimate of COPD and had methods sufficiently clear to establish what the sampling strategy was, what the diagnostic criteria were, and how the diagnosis was made.

Results

The authors found 32 sources of prevalence data, most in 17 single countries in the developed world. Most of the studies examined adults, but often with age restrictions and both younger and older ages.

Methods used to diagnose COPD included:

Prevalence estimates varied, but the largest discrepancy was between the WHO expert opinion estimate of a world prevalence of 0.8%, and all other studies where the estimate of overall prevalence was between 1% and 18%, with most between 3% and 10%. There were too many variables to determine what the differences were in different ages, or using different diagnostic methods, but there was a tendency for prevalence to be higher in men.

Estimates of prevalence where the population was large enough to be representative, in theory, of the entire population of a country, are shown in Figure 1, overall, and for men and women separately. Most estimates again were between 3% and 10%.

Figure 1: Estimates of COPD prevalence in adults

Comment

The simple answer to our simple question is that we really don’t know the prevalence of COPD with any accuracy, but it is probably more than we thought, and we probably do not play sufficient attention to it.

Definition makes profound differences. One Italian study applied various criteria used in Europe and the USA to about 2,000 people in a rural area in the Po valley aged 25 or older, and found that COPD prevalence could be as low as 11% or as high as 57%, depending on age and definition.

Definitely some fertile ground for respiratory physicians and physiologists, epidemiologists, primary care professionals, health economists and the like here.

What might this mean for a UK population, where about 40% of the population is aged 45 years or more, the age where COPD is most likely to be found? Applying the range of estimates found for COPD, this would mean between about 1,000 and 4,000 cases per 100,000 population. This not an insignificant burden.

References:

  1. RJ Halbert et al. Interpreting COPD prevalence estimates. What is the true burden of disease? Chest 2003 123: 1684-1692.

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