Tuberculosis is caused by bacteria, according to Mayo Clinic. Spread when an infected person coughs, sneezes or speaks and releases droplets into the air, tuberculosis is contagious. It is not easily transmittable from person to person, and people who live with someone infected with tuberculosis are at greatest risk.
Once someone undergoes treatment for a tuberculosis infection for two weeks, he is no longer contagious, according to Mayo Clinic. Many people with a healthy immune system are able to fight the tuberculosis bacteria, while those with a compromised immune system are at higher risk of contracting tuberculosis. Most forms of tuberculosis are treatable, but other forms have developed a resistance to drugs commonly used to treat the infection, making treatment more difficult.