because the bacteria that cause tuberculosis are transmitted through the air the disease can be contagious. but it's nearly impossible to catch tb by a single social contact with an infected person. to be at risk of being infected you must be exposed to tb bacteria constantly by living or working in close quarters with someone who has the active disease. even then because the bacteria generally stay latent (inactive) after they invade the body only 10% of people infected with tb will ever have the active disease. the remaining 90% have what's called latent tb infection -- they show no signs of infection and won't be able to spread the disease to others. these latent infections can eventually become active though so even people without symptoms should receive medical treatment. medication can help get rid of the inactive bacteria before they become active.
what causes tuberculosis?