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Population prevalence of COPD

Firestone Institute for Respiratory Health, McMaster University, Hamilton, ON, Canada.

To the Editors:

The study by Shirtcliffe et al. 1 discusses the use of various definitions of abnormal spirometric results to estimate the prevalence of chronic obstructive pulmonary disease in New Zealand and raises a major question that is not addressed in the analyses.

Childhood asthma is common and can lead to a degree of irreversible airflow obstruction in adulthood. In another New Zealand study, based on the Dunedin longitudinal population-based cohort, Sears et al. 2 reported that persistent or relapsing childhood asthma was present in 26.9% of 26-yr-old study subjects. This is not dissimilar to the prevalence of doctor-diagnosed asthma (24%) in subjects undergoing pulmonary function testing in the Wellington study. Rasmussen et al. 3 also reported that airway remodelling, based on an abnormal post-bronchodilator forced expiratory volume in one second/forced vital capacity ratio, determined as a ratio 2 SD below the mean for healthy age- and sex-matched individuals, was present in 22% of males and 10.5% of females with asthma at 26 yrs of age.

It is likely, therefore, that a proportion of subjects determined by spirometry to have "chronic obstructive pulmonary disease" in the Wellington study 1 have asthma-related impairment of lung function. The prevalence of nonasthma-related chronic obstructive pulmonary disease could be determined by excluding subjects with a history of doctor-diagnosed asthma, and if so I suspect the actual prevalence of chronic obstructive pulmonary disease, especially in the younger age groups, reported by Shirtcliffe et al. 1 as 5.6% in those aged <40 yrs and 12% among nonsmokers, would then be significantly lower than reported.

REFERENCES

1. Shirtcliffe P, Weatherall M, Marsh S, et al. COPD prevalence in a random population survey: a matter of definition. Eur Respir J 2007;30:232–239.[Abstract/Free Full Text]
2. Sears MR, Greene JM, Willan AR, et al. A longitudinal, population-based, cohort study of childhood asthma followed to adulthood. N Engl J Med 2003;349:1414–1422.[Abstract/Free Full Text]
3. Rasmussen F, Taylor DR, Flannery EM, et al. Risk factors for airway remodeling in asthma manifested by a low postbronchodilator FEV₁/vital capacity ratio: a longitudinal population study from childhood to adulthood. Am J Respir Crit Care Med 2002;165:1480–1488.[Abstract/Free Full Text]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Permissions Request Permissions Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Sears, M. R. Search for Related Content PubMed PubMed Citation Articles by Sears, M. R.