The primary outcome measure is the absolute number of COPD exacerbation days per patient per year (retrospectively defined with the daily symptom diary). In this study a COPD exacerbation is defined as ‘worsening of the patient's condition from the stable state and beyond day-to-day variations, requiring treatment with a course of oral corticosteroids and/or antibiotics’. The start of a COPD exacerbation will be defined as ‘a clear negative change in two major
symptoms (breathlessness, sputum production, sputum colour) or onemajor and one minor symptom (cough,wheeze, and fever (>38.5 °C)) from baseline, for at least two consecutive days’. The day of exacerbation resolution will be defined as the first day of:
1) three successive days that the patient has
returned to his normal health state; or
2) seven consecutive days on which the patient continuously reports no or only a slight increase in symptoms compared to baseline, with no fever
or change in sputum colour. Secondary outcome measures and other objectives are summarised in Table 1.