Confounding factors related to the incidence of chronic obstructive pulmonary disease exacerbations
| Factor | Reference |
| Sex | 34 |
| Season, weather, viral outbreaks | 18–20, 35 |
| Influenza vaccination | 35 |
| Pneumococcal vaccination | 36 |
| Pulmonary rehabilitation | 37 |
| Regular inhaled corticosteroids | 2, 31 |
| Regular long-acting bronchodilators | 38, 39 |
| Regular tiotropium | 40, 41 |
| Mucolytics/antioxidants | 42 |
| Specific antibiotic used to treat initial exacerbation (particularly activity against Haemophilus influenzae) | 43 |
| Current smoking | 43 |
| Ischaemic heart disease | 43 |