Characteristics of the study subjects
| Characteristics | Cases | Controls# |
| Subjects n | 371 | 1864 |
| Mean age yrs | 77.7±8.6 | 77.7±3.8 |
| Males | 243 (65.5) | 949 (50.8) |
| Duration of follow-up yrs | 2.5±2.2 | 2.6±1.0 |
| Medical characteristics at cohort entry | ||
| Diabetes | 60 (16.2) | 128 (7.0) |
| Systemic hypertension | 244 (65.8) | 940 (52.2) |
| Hyperlipidaemia | 16 (4.3) | 59 (3.4) |
| Ischaemic heart disease | 155 (41.8) | 332 (18.1) |
| Heart failure | 104 (28.0) | 252 (13.7) |
| COPD co-therapy¶ | ||
| Prescriptions for inhaled β-agonists</emph> | 2.2±3.6 | 2.0±1.5 |
| Prescriptions for inhaled ipratropium | 1.5±3.1 | 1.3±1.4 |
| Prescriptions for nebulised β-agonists | 1.4±4.1 | 1.2±2.1 |
| Prescriptions for theophylline | 0.9±2.7 | 0.9±1.2 |
| Daily dose of oral corticosteroids mg hydrocortisone | 3.7±11.2 | 2.3±3.1 |
| COPD exacerbations+ prior to index date | ||
| 0 | 248 (66.9) | 1320 (71) |
| 1–2 | 84 (22.6) | 411 (21.8) |
| ≥3 | 39 (10.5) | 133 (7.2) |
| Hospitalisation in the last 3 months days | ||
| None | 261 (70.4) | 1683 (90.3) |
| <7 | 61 (16.4) | 75 (4.1) |
| 7–13 | 28 (7.6) | 66 (3.6) |
| ≥14 | 21 (5.7) | 40 (2.0) |
| Aspirin at low dose | 38 (10.2) | 116 (6.6) |
| Other nonsteroidal anti-inflammatory agents | 91 (24.5) | 411 (22.3) |
Data are presented as mean±sd or n (%). COPD: chronic obstructive pulmonary disease. #: to account for the variable number of controls in each matched set, all means, sd and percentages were weighted by the inverse of the number of controls in each set; ¶: in the 12 months before index date; +: defined as the number of hospitalisations with COPD as the primary discharge diagnosis and the number of times where, within a 7-day time-window, antibiotics and corticosteroids were simultaneously prescribed.