When the infected person has TB in other organs than the lungs or throat they are not usually considered to be infectious to others. For example, a patient who has TB in the kidney or spine will not spread the disease to others even though it is an active disease.
Latent TB
There are people who breathe in the TB bacteria and do not become ill though they do present as infected when tested.
For reasons not completely understood by medical science, those people have the ability to fight the infection and not become ill. The bacteria does not grow in their bodies. Once they are infected however, the bacteria remains in that person's body indefinitely and it can eventually become active.
People with latent TB infection have no symptoms don't feel sick can't spread TB to others usually have a positive skin test reaction can develop active TB disease if they do not receive treatment for latent TB infection (Questions and answers about TB (http://www.cdc.gov/nchstp/tb/faqs/qa.htm)"
An active TB infection is defined as an infection that the immune system does not stop from growing. The bacteria attacks healthy tissue and destroys it. If the infection is in the lungs it has the ability to put a hole in the lung.
Symptoms of active TB include coughing that last three weeks or more, coughing up blood and pain in the chest. In addition, symptoms can also include weakness, fatigue, loss of appetite, developing...
If one is infected the site of the test will produce a reaction within 72 hours. If one is not infected there will be no reaction. A positive reaction at the test site does not automatically mean one has an active infection however, it simply means one has been infected. A chest x-ray is used to determine whether the person has a latent or an active infection (Questions and answers about TB (http://www.cdc.gov/nchstp/tb/faqs/qa.htm).
Conclusion
Tuberculosis is a disease that was all but eradicated in the United States until a few decades ago when it began to make a comeback. It is important that those infected with it comply with treatment so that it will not be spread. Education of the public will be a key factor in the battle against the disease.
References
Questions and answers about TB (http://www.cdc.gov/nchstp/tb/faqs/qa.htm)
Tuberculosis
http://www.cdc.gov/nchstp/tb/pubs/tboffices.htm
