TB is an infectious disease caused by a bacterium, M. tuberculosis, that spreads from person to person in tiny drops of moisture released when someone who has the active form of the disease sneezes or coughs. However, most people infected with the bacteria that causes TB don't have the active form, don't know that they're infected, and can't infect others. This inactive form of the disease can be diagnosed by injecting an antigen under the skin on the forearm and waiting to see if a red welt forms. If this skin test is positive, further tests, including a chest x-ray, need to be done to determine the status of the infection.
Most adult cases of active TB in the lungs are believed to occur from reactivation of the bacteria that were acquired months to years earlier, possibly from a change in the patient's immune defenses. Early symptoms of the active disease include disease include fatigue, weight loss, fever, night sweats, and loss of appetite. More severe symptoms include a cough, chest pain, and bloody sputum. TB can also develop in organs besides the lungs, especially the kidneys, bones, and tissues covering the brain and spinal cord.
If your friend has active TB, you can catch it from her, but you would have to spend, on average, eight hours a day for six months or 24 hours a day for two months working or living with her to become infected. Those most likely to become infected are people whose immune systems are weakened by HIV/AIDS, poor nutrition, drug addiction or other factors.
Fortunately, TB usually can be cured by long-term treatment with antibiotics. Two weeks after appropriate treatment begins, your friend will no longer be able to spread the disease to others.
Doctors prescribe a combination of antibiotics for at least six months and sometimes as long as two years. You have to take the drugs on schedule every day and can't stop taking them or miss a dose even if you feel better. If you don't take the drugs as instructed for the proper length of time, the TB bacteria can become resistant, making treatment more complicated and prolonged. Partly as a result of noncompliance with treatment, multi-drug resistant TB (MDR-TB) is becoming more common; it is difficult to cure and can be fatal.
Andrew Weil, M.D.