| Risk factor | Table column head | |
| Frequency | Percent | |
| Smoking | 138 | 27.7 |
| Overcrowding | 154 | 30.9 |
| Genetic predisposition | 59 | 11.8 |
| Immuno-compromised | 346 | 69.3 |
| Alcohol | 43 | 8.6 |
| Illegal drug use | 71 | 14.2 |