Frequency and severity of COPD exacerbations and future risk of exacerbations and mortality: an observational cohort study in Canada.

To estimate the risk of subsequent exacerbations, in relation to history of exacerbations, in a cohort of older chronic obstructive pulmonary disease (COPD) patients in Canada. Using provincial claims data from Ontario, Canada, patients with COPD aged≥65 years (identified between 2004 and 2018; followed up to 2020) were categorised into one of four mutually exclusive groups: no exacerbation; only one moderate; only one severe; or two or more exacerbations of any severity (moderate or severe) during the baseline period. The index date was the first documentation of a COPD diagnosis code; the subsequent 12 months served as the baseline period. Adjusted risks of subsequent exacerbations (any severity and severe exacerbation, separately) by the end of postbaseline year 1, 2 and 3 were estimated, accounting for differences in patient and disease characteristics and competing risk of death. A total of 591 686 patients were included. The majority (89.8%) had no exacerbation at baseline, 3.1% had one moderate exacerbation only, 3.6% had one severe exacerbation only and 3.6% had two or more exacerbations of any severity. Adjusted risks of a subsequent exacerbation of any severity by the end of year 3 were 28.6% (95% CI, 28.5% to 28.7%) with no baseline exacerbation; 56.6% (95% CI, 56.1% to 57.1%), one severe; 58.4% (95% CI, 58.0% to 58.8%), one moderate; and 77.5% (95% CI, 77.2% to 77.8%) two or more exacerbations. Adjusted risks of a subsequent severe exacerbation by the end of year 3 were 20.1% (95% CI, 20.0% to 20.2%) with no baseline exacerbation; 34.9% (95% CI, 34.5% to 35.4%), one moderate; 46.7% (95% CI, 46.2% to 47.2%), one severe; and 59.6% (95% CI, 59.3% to 60.0%) two or more exacerbations. Having a history of a single severe or two or more exacerbations of any severity is associated with a higher risk of future exacerbations, with observed exacerbation rates and severity that are constant over time. Even one moderate exacerbation over a year is associated with poorer outcomes, compared with the absence of exacerbation, and moderate exacerbations should be managed accordingly.