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Introduction
- The number of tubercle bacilli expelled in the air by a tuberculosis (TB) infected person is directly related to their infectiousness
- TB transmission is rare in children <10 years old due to their inability to expectorate sputum & low TB bacilli load in their sputum
Etiology
- Caused by Mycobacterium tuberculosis, a Gram-positive bacteria with slow growth rate that is enhanced by 6-8% CO2 & temperature of 35-40°C
Pathophysiology
- Primarily transmitted through airborne route
- Other uncommon modes of transmission: Ingestion of contaminated, unpasteurized dairy products from infected cattle (M bovis) or through skin inoculation
Risk Factors
- Tuberculosis (TB) infection in children is usually obtained from an infectious adolescent or adult depending on the closeness & length of their contact, & the index case’s severity of lung involvement & infectiousness
- Children <5 years old have increased susceptibility to TB infection
- Presence of human immunodeficiency virus (HIV) infection & malnutrition increases the risk for TB
- Requires at least 5-200 bacilli to cause an infection
- Usually takes 3 weeks to 3 months for an inhaled tubercle bacilli to cause a reactive tuberculin skin test
