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On their first point, we agree that we should be careful about terminology. We evaluated a random sample of individuals representative of the general population rather than patients, so the findings that episodes of respiratory events occurred in these subjects would likely reflect real events in the general population. Furthermore, our study definition for exacerbations was the same standard questionnaire criteria for exacerbations used in clinical trials of selected patients with COPD.3
On the second point on aetiologies for non-COPD subgroup in this study, we would like to emphasise that ‘non-COPD’ was defined by the absence of chronic airflow limitation using the standard, although arbitrary spirometric criteria. We excluded those individuals with self-reported chronic obstructive lung diseases, namely, COPD, chronic bronchitis, emphysema and asthma and evaluated bronchodilator reversibility but did not perform bronchoprovocation test. Thus, residual confounding by undiagnosed asthma or bronchiectasis remains. We could not address other specific aetiologies in this study, and further data would require linkage to administrative databases and longitudinal follow-up of the cohort.
On the third point of aetiologies for exacerbations, we do not have aetiologies for the exacerbation-like events. However, to be fair, do we really know the aetiologies for exacerbations among patients with COPD? We assume most of the causes are viral or bacterial infections, but data on causality are lacking. This is an area that requires further exploration. Our study could only address this point indirectly.
Dr Khurana and Dr Aggarwal are right to imply that more data for proper diagnosis are required; we need more evidence of the types of respiratory symptoms that best detect COPD and its onset by following up cohort subgroups with respiratory symptoms and with normal lung function or mild airflow limitation.4
Contributors WCT drafted the response and finalised it. The other authors commented on the first draft and agreed with the final document.
Funding The Canadian Cohort of Obstructive Lung Disease (COLD/CanCOLD) is funded by the Canadian Institute of Heath Research (CIHR/Rx&D Collaborative Research Program Operating Grants- 93326); industry partners Astra Zeneca Canada Ltd., Boehringer-Ingelheim Canada Ltd, GlaxoSmithKline Canada Ltd, Merck, Novartis Pharma Canada Inc., Nycomed Canada Inc., Pfizer Canada Ltd; and the Respiratory Health Network of the FRSQ. The funders had no role in the study design, data collection and analysis, decision to publish or preparation of the manuscript.
Competing interests WCT and JB report unrestricted educational grants from GlaxoSmithKline, Pfizer, Boehringer Ingelheim, AstraZeneca for the epidemiological COLD study; grants for the operations of the CanCOLD longitudinal epidemiological study from the Canadian Institute of Heath Research (CIHR/Rx&D Collaborative Research Program Operating Grants 93326) with industry partners AstraZeneca Canada, Boehringer Ingelheim Canada, GlaxoSmithKline Canada, Merck, Novartis Pharma Canada Inc., Nycomed Canada Inc., Pfizer Canada, outside the submitted work. WCT also received personal fees from GlaxoSmithKline board membership. DO'D reports grants from CIHR Research & Development during the conduct of the study. DM, an employee of the University of Saskatchewan, received funding from the Canadian Institutes of Health Research (via McGill University) to undertake this research. KRC received compensation for consulting with CSLBehring, GlaxoSmithKline, Grifols, Novartis, Roche and Takeda; has undertaken research funded by AstraZeneca, Boehringer-Ingelheim, CSLBehring, Forest Labs, GlaxoSmithKline, Johnson & Johnson, Novartis, Roche and Takeda, and has participated in continuing medical education activities sponsored in whole or in part by AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Grifols, Merck Frosst, Novartis, Nycomed, Pfizer and Talecris. PH reports grants from Canadian Institute of Health Research during the conduct of the study; grants and personal fees from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Merck, Novartis, Takeda, Grifols, CSL Behring, Pfizer, Almirall outside the submitted work. FM reports grants from GlaxoSmithKline, Boehringer Ingelheim, other from GlaxoSmithKline, Boehringer Ingelheim, Novartis, Griffols, Almirall, personal fees from Novartis, outside the submitted work. DDS reports personal fees from board membership, grants from/grants pending, personal fees from payment for lectures including service on speakers bureaus, other from travel to Denver for ATS (2011) outside the submitted work.
Ethics approval Institutional review board at each site.
Provenance and peer review Not commissioned; internally peer reviewed.