After exposure, it usually takes 8 to 10 weeks before the TB test would show if someone had become infected." "Depending on ventilation and other factors, these tiny droplets the person who has active tuberculosis can remain suspended in the air for several hours. Should another person inhale them, he or she may become infected with TB. The probability of transmission will be related to the infectiousness of the person with TB, the environment where the exposure occurred, the duration of the exposure, and the susceptibility of the host." In fact, "it isn't easy to catch TB. You need consistent exposure to the contagious person for a long time. For that reason, you're more likely to catch TB from a relative than a stranger."