Table 3

Factors determining susceptibility to tuberculosis

AgeThose 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 factorsHIV infection
Steroid therapy
Cytotoxic drugs
Post-transplant immunosuppressive therapy
Congenital immunodeficiencies
Protein energy malnutrition
Chronic medical conditionsDiabetes mellitus
Chronic liver or renal disease
Malignancies
Lung damage, especially silicosis
StressEndocrine factors
Previous exposure to mycobacteriaBCG vaccination
Exposure to environmental mycobacteria
Mycobacterial factorsVariation in strain virulence (?)
Infective dose