Clearance of air of tubercle bacilli is most effectively accomplished by good ventilation. This leads to dispersion of bacilli in a larger volume of air and reduces thus the risk of a susceptible person to inhale them. Good ventilation is easier in warm climates where windows can be kept open than in cold climates where much of the activity takes place in closed rooms. Bacilli survive indoors for a prolonged period of time. Outside, in addition to be rapidly dispersed, they are progressively killed by the ultraviolet radiation emitted by the sun.
