Host defence abnormalities leading to chronic bacterial infection of the upper and lower airways
| Host defence | Primary | Secondary |
| Cilia | Kartagener’s syndrome | Viral infection |
| Primary ciliary dyskinesia | Cigarette smoke | |
| Mucus | Young’s syndrome | Viral infection |
| Cigarette smoke | ||
| Allergy | ||
| Periciliary fluid | Cystic fibrosis | Air conditioning |
| Dehydration | ||
| Antibacterial | Common variable immunodeficiency | HIV |
| Unknown | Idiopathic bronchiectasis | Panbronchiolitis |
| Yellow nail syndrome | ||
| Ulcerative colitis |