Principal underlying diseases
| n | % | |
| None | 578 | 43.5 |
| Immune deficiencies | 139 | 10.5 |
| Pulmonary tuberculosis | 123 | 9.3 |
| Asthma | 95 | 7.2 |
| Cystic fibrosis | 68 | 5.1 |
| Congenital heart disease | 64 | 4.8 |
| Lung malformations | 61 | 4.6 |
| Bronchopulmonary dysplasia | 61 | 4.6 |
| Vascular ring | 31 | 2.3 |