Talitha L. Feenstra

A dynamic population model of disease progression in COPD

To contribute to evidence-based policy making, a dynamic Dutch population model of chronic obstructive pulmonary disease (COPD) progression was developed. The model projects incidence, prevalence, mortality, progression and costs of diagnosed COPD by the Global Initiative for Chronic Obstructive Lung Disease-severity stage for 2000–2025, taking into account population dynamics and changes in smoking prevalence over time. It was estimated that of all diagnosed COPD patients in 2000, 27% had mild, 55% moderate, 15% severe and 3% very severe COPD. The severity distribution of COPD incidence was computed to be 40% mild, 55% moderate, 4% severe and 0.1% very severe COPD. Disease progression was modelled as decline in forced expiratory voume in one second (FEV1) % predicted depending on sex, age, smoking and FEV1 % pred. The relative mortality risk of a 10-unit decrease in FEV1 % pred was estimated at 1.2. Projections of current practice were compared with projections assuming that each year 25% of all COPD patients receive either minimal smoking cessation counselling or intensive counselling plus bupropion. In the projections of current practice, prevalence rates between 2000–2025 changed from 5.1 to 11 per 1,000 inhabitants for mild, 11 to 14 per 1,000 for moderate, 3.0 to 3.9 per 1,000 for severe and from 0.5 to 1.3 per 1,000 for very severe COPD. Costs per inhabitant increased from #8364;1.40 to 3.10 for mild, #8364;6.50 to 9.00 for moderate, #8364;6.20 to 8.50 for severe and from #8364;3.40 to 9.40 for very severe COPD (price level 2000). Both smoking cessation scenarios were cost-effective with minimal counselling generating net savings. In conclusion, the chronic obstructive pulmonary disease progression model is a useful instrument to give detailed information about the future burden of chronic obstructive pulmonary disease and to assess the long-term impact of interventions on this burden.

Case fatality of COPD exacerbations: A meta-analysis and statistical modelling approach

The aim of our study was to estimate the case fatality of a severe exacerbation from long-term survival data presented in the literature. A literature search identified studies reporting ≥1.5 yr survival after a severe chronic obstructive pulmonary disease (COPD) exacerbation resulting in hospitalisation. The survival curve of each study was divided into a critical and a stable period. Mortality during the stable period was then estimated by extrapolating the survival curve during the stable period back to the time of exacerbation onset. Case fatality was defined as the excess mortality that results from an exacerbation and was calculated as 1 minus the (backwardly) extrapolated survival during the stable period at the time of exacerbation onset. The 95% confidence intervals (CI) of the estimated case fatalities were obtained by bootstrapping. A random effect model was used to combine all estimates into a weighted average with 95% CI. The meta-analysis based on six studies that fulfilled the inclusion criteria resulted in a weighted average case-fatality rate of 15.6% (95% CI 10.9–20.3), ranging from 11.4% to 19.0% for the individual studies. A severe COPD exacerbation requiring hospitalisation not only results in higher mortality risks during hospitalisation, but also in the time-period after discharge and contributes substantially to total COPD mortality.