3. How People are Exposed to TB Bacilli?

• When someone with pulmonary TB coughs, invisible droplets containing TB bacilli are dispersed into the air;
• The remain suspended in the air and fall at a rate of 12mm/hr; and
• These droplets can then be inhaled by others.

Transmission generally occurs indoors, in dark, damp spaces where the bacilli can survive for several hours. Direct sunlight has a bactericidal effect on the tubercle bacilli. Close contact with a person who has infectious PTB for a prolonged time increases the risk of transmission.