Tuberculosis (TB) is caused by Mycobacterium tuberculosis, a gram-positive bacteria with slow growth rate that is enhanced by 6-8% carbon dioxide and temperature of 35-40ºC.
It is primarily transmitted through airborne route.
The number of tubercle bacilli expelled in the air by a 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 and low TB bacilli load in their sputum.
TB infection in children is usually obtained from an infectious adolescent or adult depending on the closeness and length of contact and the index case's severity of lung involvement and infectiousness.