Incidence of utilization- and symptom-defined COPD exacerbations in hospital- and population-recruited patients

Abstract

Objectives

The objectives of this study were to estimate the impact of recruitment source and outcome definition on the incidence of acute exacerbations of COPD (AECOPD) and explore possible predictors of AECOPD.

Patients and methods

During a 1-year follow-up, we performed a baseline visit and four telephone interviews of 81 COPD patients and 132 controls recruited from a population-based survey and 205 hospital-recruited COPD patients. Both a definition based on health care utilization and a symptom-based definition of AECOPD were applied. For multivariate analyses, we chose a negative binomial regression model.

Results

COPD patients from the population- and hospital-based samples experienced on average 0.4 utilization-defined and 2.9 symptom-defined versus 1.0 and 5.9 annual exacerbations, respectively. The incidence rate ratios for utilization-defined AECOPD were 2.45 (95% CI 1.22–4.95), 3.43 (95% CI 1.59–7.38), and 5.67 (95% CI 2.58–12.48) with Global Initiative on Obstructive Lung Disease spirometric stages II, III, and IV, respectively. The corresponding incidence rate ratios for the symptom-based definition were 3.08 (95% CI 1.96–4.84), 3.45 (95% CI 1.92–6.18), and 4.00 (95% CI 2.09–7.66). Maintenance therapy (regular long-acting muscarinic antagonists, long-acting beta-2 agonists, inhaled corticosteroids, or theophylline) also increased the risk of AECOPD with both exacerbation definitions (incidence rate ratios 1.65 and 1.73, respectively). The risk of AECOPD was 59%–78% higher in the hospital sample than in the population sample.

Conclusion

If externally valid conclusions are to be made regarding incidence and predictors of AECOPD, studies should be based on general population samples or adjustments should be made on account of a likely higher incidence in other samples. Likewise, the effect of different AECOPD definitions should be taken into consideration.

Keywords:

• COPD
• exacerbations
• general population
• predictors

Supplementary materials

Table S1 Number of events of exacerbations of respiratory symptoms in population-recruited cases by sex, age, smoking status, education, and FEV₁% predicted

Table S2 Number of events of exacerbations of respiratory symptoms in hospital-recruited cases by sex, age, smoking status, education, and FEV₁% predicted

Table S3 IRRs (95% CI) for AECOPD with a resource-based exacerbation definition

Table S4 IRRs (95% CI) for AECOPD with a symptom-based exacerbation definition

Acknowledgments

The authors are indebted to Margrete Klemmetsby, Hege Marie Schnelle, Idunn Riisnes, Jan Egil Romestrand, Erik Helgeland, Jan Schille, Lene Svendsen, Tonje Lauvaasvaag, Heike Wiegmann, and Lene Kvamsdal for their contribution in collecting the data for EconCOPD. ME has recently received a research grant from AstraZeneca. Within the last 3 years, TME has received travel grants from InterMune for the AIR conferences, a grant for the MicroILD study from Boehringer Ingelheim, and speaker fees from AstraZeneca and Boehringer Ingelheim. RG reports grants from the Norwegian Association of Heart and Lung Patients and EXTRA funds from the Norwegian Foundation for Health and Rehabilitation as well as YaraPraxair during the conduct of the study, grants and personal fees from Boehringer Ingelheim, personal fees from AstraZeneca, and personal fees from GlaxoSmithKline outside the submitted work. AG has during the last 3 years participated in the advisory boards of Chesi Pharma AS, Sverige, Novartis Norge AS, Takeda Nycomed Norge, AstraZeneca Norge, and Boehringer Ingelheim, Norway. The Norway GenKOLS study, where he was the principal investigator, was supported by GlaxoSmithKline Research & Development Limited, UK.

Author contributions

Design, planning, and data collection were carried out by RG, AG, and AJ. Data management and quality control was performed by ME and RG. Statistical analyses were carried out by ME, RG, AJ, and TME. Analysis planning was done by RG, AJ, and ME. Drafting was carried out by ME. Revision and approval of drafts were performed by RG, TME, AJ, AG, PB, and ME. All authors contributed toward data analysis, drafting and critically revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.