The Obstructive Lung Disease in Northern Sweden Chronic Obstructive Pulmonary Disease Study: design, the first year...

Most epidemiological data on chronic obstructive pulmonary disease (COPD) are cross-sectional, and the longitudinal course of disease on population bases is incompletely described.

To describe an epidemiological study designed to follow the longitudinal course of disease in chronic obstructive lung disease, COPD, including co-morbidity and mortality and further, to evaluate the impact of COPD on quality of life and health economics.

From the Obstructive Lung Disease in Northern Sweden studies database cohorts I-IV, all subjects with COPD according to the Global Initiative for Chronic Obstructive Lung Disease spirometric criteria, FEV(1)/FVC < 0.70 (n = 993), were identified together with a similar size age- and gender-matched control group. The study population was invited to a yearly examination starting in year 2005. The examinations included structured interview, spirometry with reversibility testing, oxygen saturation and health-related quality of life questionnaires.

On the first year, 83% of the population was examined, and the subjects unable to attend the examination were interviewed by telephone. Altogether, 91% of the original study population participated (95% of all subjects were alive at the end of the first year). Mortality was significantly higher among subjects with COPD, 5.1%, compared with controls, 3.0% (P = 0.018).

The study design including cases of COPD representative of COPD by disease severity in the general population and a similar sized control group, together with a high participation rate in the first study year, creates excellent conditions for evaluating the impact of COPD on population bases, and to follow the longitudinal course of disease in COPD.