Factors determining susceptibility to tuberculosis
| Age | Those aged less than 5 years and the elderly are susceptible |
| The 5–15 age group is relatively protected | |
| Racial and genetic predisposition | “Herd immunity” |
| ? HLA | |
| ? Cytokine gene defects | |
| Immunological factors | HIV infection |
| Steroid therapy | |
| Cytotoxic drugs | |
| Post-transplant immunosuppressive therapy | |
| Congenital immunodeficiencies | |
| Protein energy malnutrition | |
| Chronic medical conditions | Diabetes mellitus |
| Chronic liver or renal disease | |
| Malignancies | |
| Lung damage, especially silicosis | |
| Stress | Endocrine factors |
| Previous exposure to mycobacteria | BCG vaccination |
| Exposure to environmental mycobacteria | |
| Mycobacterial factors | Variation in strain virulence (?) |
| Infective dose |